diff --git a/backend/.env.example b/backend/.env.example
index 1581b25..c3a1fde 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -18,16 +18,16 @@ CH_COS_BUCKET=hku-icb-1311994147
 CH_COS_BASE_URL=https://hku-icb-1311994147.cos.ap-guangzhou.myqcloud.com
 
 # SMTP Email
-CH_SMTP_HOST=
+CH_SMTP_HOST=gz-smtp.qcloudmail.com
 CH_SMTP_PORT=465
-CH_SMTP_USER=
-CH_SMTP_PASSWORD=
-CH_SMTP_FROM_EMAIL=
-CH_SMTP_FROM_NAME=HKU ICB
+CH_SMTP_USER=noreply
+CH_SMTP_PASSWORD=hX2gqEPjaRhULXF69
+CH_SMTP_FROM_EMAIL=noreply@hkuicb.info
+CH_SMTP_FROM_NAME=HKU ICB Class Hub
 
 # Frontend URL
 CH_FRONTEND_URL=http://localhost:3000
 
 # Super Admin Seed
-CH_SUPER_ADMIN_EMAIL=admin@classhub.com
+CH_SUPER_ADMIN_EMAIL=admin@hkuicb.info
 CH_SUPER_ADMIN_PASSWORD=admin123
diff --git a/backend/alembic/env.py b/backend/alembic/env.py
index 96e3e0c..21a77bf 100644
--- a/backend/alembic/env.py
+++ b/backend/alembic/env.py
@@ -7,7 +7,7 @@ from sqlalchemy.ext.asyncio import async_engine_from_config
 
 from app.config import settings
 from app.db.base import Base
-from app.db.models import Class_, User, Timeline, Schedule  # noqa: ensure models registered
+from app.db.models import Class_, User, Timeline, Schedule, Announcement, Resource, Notification  # noqa: ensure models registered
 
 config = context.config
 config.set_main_option("sqlalchemy.url", settings.database_url)
diff --git a/backend/app/api/announcements.py b/backend/app/api/announcements.py
new file mode 100644
index 0000000..e8a2671
--- /dev/null
+++ b/backend/app/api/announcements.py
@@ -0,0 +1,121 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.deps import require_role
+from app.db.database import get_db
+from app.db.models import User
+from app.schemas.announcement import AnnouncementCreate, AnnouncementUpdate, AnnouncementOut
+from app.schemas.common import PageResponse
+from app.services.announcement_service import (
+    create_announcement,
+    update_announcement,
+    delete_announcement,
+    get_announcement_by_id,
+    list_announcements,
+)
+
+router = APIRouter(prefix="/api/announcements", tags=["announcements"])
+
+
+@router.get("/", response_model=PageResponse[AnnouncementOut])
+async def get_announcements(
+    page: int = 1,
+    page_size: int = 20,
+    class_id: int | None = None,
+    user: User = Depends(require_role("super_admin", "class_admin", "student")),
+    db: AsyncSession = Depends(get_db),
+):
+    effective_class_id = class_id if user.role == "super_admin" and class_id else user.class_id
+    if effective_class_id is None:
+        return PageResponse(items=[], total=0, page=page, page_size=page_size, total_pages=0)
+
+    announcements, total = await list_announcements(db, effective_class_id, page, page_size)
+    total_pages = (total + page_size - 1) // page_size
+
+    items = []
+    for a in announcements:
+        items.append(
+            AnnouncementOut(
+                id=a.id,
+                class_id=a.class_id,
+                author_id=a.author_id,
+                author_name=a.author.name if a.author else "Unknown",
+                title=a.title,
+                content=a.content,
+                is_pinned=a.is_pinned,
+                created_at=a.created_at,
+                updated_at=a.updated_at,
+            )
+        )
+
+    return PageResponse(
+        items=items, total=total, page=page, page_size=page_size, total_pages=total_pages
+    )
+
+
+@router.post("/", response_model=AnnouncementOut)
+async def create_new_announcement(
+    data: AnnouncementCreate,
+    class_id: int | None = None,
+    user: User = Depends(require_role("super_admin", "class_admin")),
+    db: AsyncSession = Depends(get_db),
+):
+    effective_class_id = class_id if user.role == "super_admin" and class_id else user.class_id
+    if effective_class_id is None:
+        raise HTTPException(status_code=400, detail="You are not assigned to a class")
+
+    announcement = await create_announcement(db, effective_class_id, user.id, data)
+    return AnnouncementOut(
+        id=announcement.id,
+        class_id=announcement.class_id,
+        author_id=announcement.author_id,
+        author_name=user.name,
+        title=announcement.title,
+        content=announcement.content,
+        is_pinned=announcement.is_pinned,
+        created_at=announcement.created_at,
+        updated_at=announcement.updated_at,
+    )
+
+
+@router.put("/{announcement_id}", response_model=AnnouncementOut)
+async def update_existing_announcement(
+    announcement_id: int,
+    data: AnnouncementUpdate,
+    user: User = Depends(require_role("super_admin", "class_admin")),
+    db: AsyncSession = Depends(get_db),
+):
+    announcement = await get_announcement_by_id(db, announcement_id)
+    if announcement is None:
+        raise HTTPException(status_code=404, detail="Announcement not found")
+    if user.role != "super_admin" and announcement.class_id != user.class_id:
+        raise HTTPException(status_code=403, detail="Access denied")
+
+    updated = await update_announcement(db, announcement, data)
+    return AnnouncementOut(
+        id=updated.id,
+        class_id=updated.class_id,
+        author_id=updated.author_id,
+        author_name=updated.author.name if updated.author else user.name,
+        title=updated.title,
+        content=updated.content,
+        is_pinned=updated.is_pinned,
+        created_at=updated.created_at,
+        updated_at=updated.updated_at,
+    )
+
+
+@router.delete("/{announcement_id}")
+async def delete_existing_announcement(
+    announcement_id: int,
+    user: User = Depends(require_role("super_admin", "class_admin")),
+    db: AsyncSession = Depends(get_db),
+):
+    announcement = await get_announcement_by_id(db, announcement_id)
+    if announcement is None:
+        raise HTTPException(status_code=404, detail="Announcement not found")
+    if user.role != "super_admin" and announcement.class_id != user.class_id:
+        raise HTTPException(status_code=403, detail="Access denied")
+
+    await delete_announcement(db, announcement)
+    return {"message": "Announcement deleted"}
diff --git a/backend/app/api/notifications.py b/backend/app/api/notifications.py
new file mode 100644
index 0000000..2d6e64a
--- /dev/null
+++ b/backend/app/api/notifications.py
@@ -0,0 +1,74 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.deps import get_current_user
+from app.db.database import get_db
+from app.db.models import User
+from app.schemas.notification import NotificationOut, UnreadCount
+from app.schemas.common import PageResponse
+from app.services.notification_service import (
+    list_notifications,
+    get_unread_count,
+    mark_as_read,
+    mark_all_as_read,
+)
+
+router = APIRouter(prefix="/api/notifications", tags=["notifications"])
+
+
+@router.get("/", response_model=PageResponse[NotificationOut])
+async def get_notifications(
+    page: int = 1,
+    page_size: int = 20,
+    user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    notifications, total = await list_notifications(db, user.id, page, page_size)
+    total_pages = (total + page_size - 1) // page_size
+
+    items = [
+        NotificationOut(
+            id=n.id,
+            type=n.type,
+            title=n.title,
+            content=n.content,
+            related_id=n.related_id,
+            is_read=n.is_read,
+            created_at=n.created_at,
+        )
+        for n in notifications
+    ]
+
+    return PageResponse(
+        items=items, total=total, page=page, page_size=page_size, total_pages=total_pages
+    )
+
+
+@router.get("/unread-count", response_model=UnreadCount)
+async def get_unread_count_api(
+    user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    count = await get_unread_count(db, user.id)
+    return UnreadCount(count=count)
+
+
+@router.put("/{notification_id}/read")
+async def mark_notification_read(
+    notification_id: int,
+    user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    success = await mark_as_read(db, notification_id, user.id)
+    if not success:
+        raise HTTPException(status_code=404, detail="Notification not found")
+    return {"message": "Marked as read"}
+
+
+@router.put("/read-all")
+async def mark_all_notifications_read(
+    user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    count = await mark_all_as_read(db, user.id)
+    return {"message": f"Marked {count} notifications as read"}
diff --git a/backend/app/api/resources.py b/backend/app/api/resources.py
new file mode 100644
index 0000000..e3f231f
--- /dev/null
+++ b/backend/app/api/resources.py
@@ -0,0 +1,153 @@
+from fastapi import APIRouter, Depends, HTTPException, UploadFile, File
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.deps import require_role
+from app.db.database import get_db
+from app.db.models import User
+from app.schemas.resource import ResourceCreate, ResourceOut
+from app.schemas.common import PageResponse
+from app.services.resource_service import (
+    create_resource,
+    list_resources,
+    get_resource_by_id,
+    increment_download_count,
+    delete_resource,
+)
+from app.services.cos_service import upload_file
+
+router = APIRouter(prefix="/api/resources", tags=["resources"])
+
+ALLOWED_FILE_TYPES = {
+    "application/pdf",
+    "application/msword",
+    "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+    "application/vnd.ms-excel",
+    "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+    "application/vnd.ms-powerpoint",
+    "application/vnd.openxmlformats-officedocument.presentationml.presentation",
+    "application/zip",
+    "text/plain",
+    "image/jpeg",
+    "image/png",
+    "image/gif",
+    "image/webp",
+}
+
+
+@router.get("/", response_model=PageResponse[ResourceOut])
+async def get_resources(
+    page: int = 1,
+    page_size: int = 20,
+    category: str | None = None,
+    class_id: int | None = None,
+    user: User = Depends(require_role("super_admin", "class_admin", "student")),
+    db: AsyncSession = Depends(get_db),
+):
+    effective_class_id = class_id if user.role == "super_admin" and class_id else user.class_id
+    if effective_class_id is None:
+        return PageResponse(items=[], total=0, page=page, page_size=page_size, total_pages=0)
+
+    resources, total = await list_resources(db, effective_class_id, category, page, page_size)
+    total_pages = (total + page_size - 1) // page_size
+
+    items = []
+    for r in resources:
+        items.append(
+            ResourceOut(
+                id=r.id,
+                class_id=r.class_id,
+                uploader_id=r.uploader_id,
+                uploader_name=r.uploader.name if r.uploader else "Unknown",
+                title=r.title,
+                description=r.description,
+                file_url=r.file_url,
+                file_type=r.file_type,
+                file_size=r.file_size,
+                category=r.category,
+                download_count=r.download_count,
+                created_at=r.created_at,
+            )
+        )
+
+    return PageResponse(
+        items=items, total=total, page=page, page_size=page_size, total_pages=total_pages
+    )
+
+
+@router.post("/", response_model=ResourceOut)
+async def upload_new_resource(
+    title: str,
+    category: str,
+    file: UploadFile = File(...),
+    description: str | None = None,
+    class_id: int | None = None,
+    user: User = Depends(require_role("super_admin", "class_admin")),
+    db: AsyncSession = Depends(get_db),
+):
+    effective_class_id = class_id if user.role == "super_admin" and class_id else user.class_id
+    if effective_class_id is None:
+        raise HTTPException(status_code=400, detail="You are not assigned to a class")
+
+    contents = await file.read()
+    if len(contents) > 50 * 1024 * 1024:  # 50MB limit
+        raise HTTPException(status_code=400, detail="File too large (max 50MB)")
+
+    if file.content_type not in ALLOWED_FILE_TYPES:
+        raise HTTPException(status_code=400, detail=f"File type {file.content_type} not allowed")
+
+    file_url = upload_file(
+        f"resources/{effective_class_id}",
+        file.filename or "file",
+        contents,
+        file.content_type,
+    )
+
+    data = ResourceCreate(title=title, description=description, category=category)
+    resource = await create_resource(
+        db, effective_class_id, user.id, data, file_url, file.content_type, len(contents)
+    )
+
+    return ResourceOut(
+        id=resource.id,
+        class_id=resource.class_id,
+        uploader_id=resource.uploader_id,
+        uploader_name=user.name,
+        title=resource.title,
+        description=resource.description,
+        file_url=resource.file_url,
+        file_type=resource.file_type,
+        file_size=resource.file_size,
+        category=resource.category,
+        download_count=resource.download_count,
+        created_at=resource.created_at,
+    )
+
+
+@router.post("/{resource_id}/download")
+async def download_resource(
+    resource_id: int,
+    user: User = Depends(require_role("super_admin", "class_admin", "student")),
+    db: AsyncSession = Depends(get_db),
+):
+    resource = await get_resource_by_id(db, resource_id)
+    if resource is None:
+        raise HTTPException(status_code=404, detail="Resource not found")
+
+    await increment_download_count(db, resource)
+    return {"file_url": resource.file_url}
+
+
+@router.delete("/{resource_id}")
+async def delete_existing_resource(
+    resource_id: int,
+    user: User = Depends(require_role("super_admin", "class_admin")),
+    db: AsyncSession = Depends(get_db),
+):
+    resource = await get_resource_by_id(db, resource_id)
+    if resource is None:
+        raise HTTPException(status_code=404, detail="Resource not found")
+    if user.role != "super_admin" and resource.class_id != user.class_id:
+        raise HTTPException(status_code=403, detail="Access denied")
+
+    await delete_resource(db, resource)
+    return {"message": "Resource deleted"}
diff --git a/backend/app/db/models.py b/backend/app/db/models.py
index cd2ff6c..59f8187 100644
--- a/backend/app/db/models.py
+++ b/backend/app/db/models.py
@@ -1,7 +1,7 @@
 import json
 from datetime import datetime
 
-from sqlalchemy import String, Text, Integer, DateTime, ForeignKey, func
+from sqlalchemy import String, Text, Integer, DateTime, Boolean, ForeignKey, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.db.base import Base
@@ -26,6 +26,12 @@ class Class_(Base):
     schedules: Mapped[list["Schedule"]] = relationship(
         "Schedule", back_populates="class_", cascade="all, delete-orphan"
     )
+    announcements: Mapped[list["Announcement"]] = relationship(
+        "Announcement", back_populates="class_", cascade="all, delete-orphan"
+    )
+    resources: Mapped[list["Resource"]] = relationship(
+        "Resource", back_populates="class_", cascade="all, delete-orphan"
+    )
 
 
 class User(Base):
@@ -131,3 +137,65 @@ class Schedule(Base):
     )
 
     class_: Mapped["Class_"] = relationship("Class_", back_populates="schedules")
+
+
+class Announcement(Base):
+    __tablename__ = "announcements"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    class_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("classes.id"), nullable=False, index=True
+    )
+    author_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id"), nullable=False
+    )
+    title: Mapped[str] = mapped_column(String(200), nullable=False)
+    content: Mapped[str | None] = mapped_column(Text, nullable=True)
+    is_pinned: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime, server_default=func.now(), onupdate=func.now()
+    )
+
+    class_: Mapped["Class_"] = relationship("Class_", back_populates="announcements")
+    author: Mapped["User"] = relationship("User")
+
+
+class Resource(Base):
+    __tablename__ = "resources"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    class_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("classes.id"), nullable=False, index=True
+    )
+    uploader_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id"), nullable=False
+    )
+    title: Mapped[str] = mapped_column(String(200), nullable=False)
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    file_url: Mapped[str] = mapped_column(Text, nullable=False)
+    file_type: Mapped[str] = mapped_column(String(50), nullable=False)
+    file_size: Mapped[int] = mapped_column(Integer, nullable=False)
+    category: Mapped[str] = mapped_column(String(50), nullable=False)
+    download_count: Mapped[int] = mapped_column(Integer, default=0, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())
+
+    class_: Mapped["Class_"] = relationship("Class_", back_populates="resources")
+    uploader: Mapped["User"] = relationship("User")
+
+
+class Notification(Base):
+    __tablename__ = "notifications"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id"), nullable=False, index=True
+    )
+    type: Mapped[str] = mapped_column(String(50), nullable=False)
+    title: Mapped[str] = mapped_column(String(200), nullable=False)
+    content: Mapped[str | None] = mapped_column(Text, nullable=True)
+    related_id: Mapped[int | None] = mapped_column(Integer, nullable=True)
+    is_read: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())
+
+    user: Mapped["User"] = relationship("User")
diff --git a/backend/app/main.py b/backend/app/main.py
index 2ee5459..4a10041 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -6,7 +6,7 @@ from fastapi.middleware.cors import CORSMiddleware
 
 from app.config import settings
 from app.db.database import create_tables
-from app.api import auth, users, classes, directory, timeline, schedule, upload
+from app.api import auth, users, classes, directory, timeline, schedule, upload, announcements, resources, notifications
 
 logging.basicConfig(
     level=logging.DEBUG if settings.debug else logging.INFO,
@@ -87,6 +87,9 @@ app.include_router(directory.router)
 app.include_router(timeline.router)
 app.include_router(schedule.router)
 app.include_router(upload.router)
+app.include_router(announcements.router)
+app.include_router(resources.router)
+app.include_router(notifications.router)
 
 
 @app.get("/api/health")
diff --git a/backend/app/schemas/announcement.py b/backend/app/schemas/announcement.py
new file mode 100644
index 0000000..6a846ea
--- /dev/null
+++ b/backend/app/schemas/announcement.py
@@ -0,0 +1,27 @@
+from datetime import datetime
+
+from pydantic import BaseModel
+
+
+class AnnouncementCreate(BaseModel):
+    title: str
+    content: str | None = None
+    is_pinned: bool = False
+
+
+class AnnouncementUpdate(BaseModel):
+    title: str | None = None
+    content: str | None = None
+    is_pinned: bool | None = None
+
+
+class AnnouncementOut(BaseModel):
+    id: int
+    class_id: int
+    author_id: int
+    author_name: str
+    title: str
+    content: str | None
+    is_pinned: bool
+    created_at: datetime
+    updated_at: datetime
diff --git a/backend/app/schemas/notification.py b/backend/app/schemas/notification.py
new file mode 100644
index 0000000..46eec08
--- /dev/null
+++ b/backend/app/schemas/notification.py
@@ -0,0 +1,17 @@
+from datetime import datetime
+
+from pydantic import BaseModel
+
+
+class NotificationOut(BaseModel):
+    id: int
+    type: str
+    title: str
+    content: str | None
+    related_id: int | None
+    is_read: bool
+    created_at: datetime
+
+
+class UnreadCount(BaseModel):
+    count: int
diff --git a/backend/app/schemas/resource.py b/backend/app/schemas/resource.py
new file mode 100644
index 0000000..fd5405e
--- /dev/null
+++ b/backend/app/schemas/resource.py
@@ -0,0 +1,24 @@
+from datetime import datetime
+
+from pydantic import BaseModel
+
+
+class ResourceCreate(BaseModel):
+    title: str
+    description: str | None = None
+    category: str  # "course_material" | "assignment" | "reading" | "other"
+
+
+class ResourceOut(BaseModel):
+    id: int
+    class_id: int
+    uploader_id: int
+    uploader_name: str
+    title: str
+    description: str | None
+    file_url: str
+    file_type: str
+    file_size: int
+    category: str
+    download_count: int
+    created_at: datetime
diff --git a/backend/app/services/announcement_service.py b/backend/app/services/announcement_service.py
new file mode 100644
index 0000000..424a849
--- /dev/null
+++ b/backend/app/services/announcement_service.py
@@ -0,0 +1,74 @@
+from sqlalchemy import select, func
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
+
+from app.db.models import Announcement, User
+from app.schemas.announcement import AnnouncementCreate, AnnouncementUpdate
+from app.services.notification_service import create_notifications_for_class
+
+
+async def create_announcement(
+    db: AsyncSession, class_id: int, author_id: int, data: AnnouncementCreate
+) -> Announcement:
+    announcement = Announcement(
+        class_id=class_id,
+        author_id=author_id,
+        title=data.title,
+        content=data.content,
+        is_pinned=data.is_pinned,
+    )
+    db.add(announcement)
+    await db.commit()
+    await db.refresh(announcement)
+
+    # Send notifications to class members
+    await create_notifications_for_class(
+        db, class_id, "announcement", f"新公告: {data.title}",
+        related_id=announcement.id, exclude_user_id=author_id,
+    )
+
+    return announcement
+
+
+async def update_announcement(
+    db: AsyncSession, announcement: Announcement, data: AnnouncementUpdate
+) -> Announcement:
+    for field, value in data.model_dump(exclude_unset=True).items():
+        setattr(announcement, field, value)
+    await db.commit()
+    await db.refresh(announcement)
+    return announcement
+
+
+async def delete_announcement(db: AsyncSession, announcement: Announcement):
+    await db.delete(announcement)
+    await db.commit()
+
+
+async def get_announcement_by_id(db: AsyncSession, announcement_id: int) -> Announcement | None:
+    result = await db.execute(
+        select(Announcement)
+        .options(selectinload(Announcement.author))
+        .where(Announcement.id == announcement_id)
+    )
+    return result.scalar_one_or_none()
+
+
+async def list_announcements(
+    db: AsyncSession, class_id: int, page: int = 1, page_size: int = 20
+) -> tuple[list[Announcement], int]:
+    total_result = await db.execute(
+        select(func.count(Announcement.id)).where(Announcement.class_id == class_id)
+    )
+    total = total_result.scalar() or 0
+
+    result = await db.execute(
+        select(Announcement)
+        .options(selectinload(Announcement.author))
+        .where(Announcement.class_id == class_id)
+        .order_by(Announcement.is_pinned.desc(), Announcement.created_at.desc())
+        .offset((page - 1) * page_size)
+        .limit(page_size)
+    )
+    announcements = list(result.scalars().all())
+    return announcements, total
diff --git a/backend/app/services/cos_service.py b/backend/app/services/cos_service.py
index 298ca3c..2fbd850 100644
--- a/backend/app/services/cos_service.py
+++ b/backend/app/services/cos_service.py
@@ -46,3 +46,30 @@ def upload_image(prefix: str, filename: str, data: bytes, content_type: str) ->
     key = f"{prefix}/{date_path}/{unique_name}{ext}"
 
     return upload_bytes(key, data, content_type)
+
+
+FILE_TYPE_EXTENSIONS = {
+    "application/pdf": ".pdf",
+    "application/msword": ".doc",
+    "application/vnd.openxmlformats-officedocument.wordprocessingml.document": ".docx",
+    "application/vnd.ms-excel": ".xls",
+    "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet": ".xlsx",
+    "application/vnd.ms-powerpoint": ".ppt",
+    "application/vnd.openxmlformats-officedocument.presentationml.presentation": ".pptx",
+    "application/zip": ".zip",
+    "text/plain": ".txt",
+    "image/jpeg": ".jpg",
+    "image/png": ".png",
+    "image/gif": ".gif",
+    "image/webp": ".webp",
+}
+
+
+def upload_file(prefix: str, filename: str, data: bytes, content_type: str) -> str:
+    """Upload any allowed file type to COS. Returns the public URL."""
+    ext = FILE_TYPE_EXTENSIONS.get(content_type, "")
+    date_path = datetime.now().strftime("%Y/%m/%d")
+    unique_name = uuid.uuid4().hex[:12]
+    key = f"{prefix}/{date_path}/{unique_name}{ext}"
+
+    return upload_bytes(key, data, content_type)
diff --git a/backend/app/services/notification_service.py b/backend/app/services/notification_service.py
new file mode 100644
index 0000000..697941c
--- /dev/null
+++ b/backend/app/services/notification_service.py
@@ -0,0 +1,107 @@
+from sqlalchemy import select, func, update
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.db.models import Notification, User
+
+
+async def create_notification(
+    db: AsyncSession,
+    user_id: int,
+    type: str,
+    title: str,
+    content: str | None = None,
+    related_id: int | None = None,
+) -> Notification:
+    notification = Notification(
+        user_id=user_id,
+        type=type,
+        title=title,
+        content=content,
+        related_id=related_id,
+    )
+    db.add(notification)
+    await db.commit()
+    await db.refresh(notification)
+    return notification
+
+
+async def create_notifications_for_class(
+    db: AsyncSession,
+    class_id: int,
+    type: str,
+    title: str,
+    content: str | None = None,
+    related_id: int | None = None,
+    exclude_user_id: int | None = None,
+):
+    """Create notifications for all approved users in a class."""
+    result = await db.execute(
+        select(User.id).where(
+            User.class_id == class_id,
+            User.status == "approved",
+        )
+    )
+    user_ids = [row[0] for row in result.all()]
+
+    for uid in user_ids:
+        if exclude_user_id and uid == exclude_user_id:
+            continue
+        notification = Notification(
+            user_id=uid,
+            type=type,
+            title=title,
+            content=content,
+            related_id=related_id,
+        )
+        db.add(notification)
+
+    await db.commit()
+
+
+async def list_notifications(
+    db: AsyncSession, user_id: int, page: int = 1, page_size: int = 20
+) -> tuple[list[Notification], int]:
+    total_result = await db.execute(
+        select(func.count(Notification.id)).where(Notification.user_id == user_id)
+    )
+    total = total_result.scalar() or 0
+
+    result = await db.execute(
+        select(Notification)
+        .where(Notification.user_id == user_id)
+        .order_by(Notification.created_at.desc())
+        .offset((page - 1) * page_size)
+        .limit(page_size)
+    )
+    notifications = list(result.scalars().all())
+    return notifications, total
+
+
+async def get_unread_count(db: AsyncSession, user_id: int) -> int:
+    result = await db.execute(
+        select(func.count(Notification.id)).where(
+            Notification.user_id == user_id,
+            Notification.is_read == False,
+        )
+    )
+    return result.scalar() or 0
+
+
+async def mark_as_read(db: AsyncSession, notification_id: int, user_id: int) -> bool:
+    result = await db.execute(
+        update(Notification)
+        .where(Notification.id == notification_id, Notification.user_id == user_id)
+        .values(is_read=True)
+    )
+    await db.commit()
+    return result.rowcount > 0
+
+
+async def mark_all_as_read(db: AsyncSession, user_id: int) -> int:
+    result = await db.execute(
+        update(Notification)
+        .where(Notification.user_id == user_id, Notification.is_read == False)
+        .values(is_read=True)
+    )
+    await db.commit()
+    return result.rowcount
diff --git a/backend/app/services/resource_service.py b/backend/app/services/resource_service.py
new file mode 100644
index 0000000..747a32f
--- /dev/null
+++ b/backend/app/services/resource_service.py
@@ -0,0 +1,75 @@
+from sqlalchemy import select, func
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
+
+from app.db.models import Resource, User
+from app.schemas.resource import ResourceCreate
+
+
+async def create_resource(
+    db: AsyncSession,
+    class_id: int,
+    uploader_id: int,
+    data: ResourceCreate,
+    file_url: str,
+    file_type: str,
+    file_size: int,
+) -> Resource:
+    resource = Resource(
+        class_id=class_id,
+        uploader_id=uploader_id,
+        title=data.title,
+        description=data.description,
+        file_url=file_url,
+        file_type=file_type,
+        file_size=file_size,
+        category=data.category,
+    )
+    db.add(resource)
+    await db.commit()
+    await db.refresh(resource)
+    return resource
+
+
+async def list_resources(
+    db: AsyncSession, class_id: int, category: str | None = None, page: int = 1, page_size: int = 20
+) -> tuple[list[Resource], int]:
+    query = select(Resource).where(Resource.class_id == class_id)
+    count_query = select(func.count(Resource.id)).where(Resource.class_id == class_id)
+
+    if category:
+        query = query.where(Resource.category == category)
+        count_query = count_query.where(Resource.category == category)
+
+    total_result = await db.execute(count_query)
+    total = total_result.scalar() or 0
+
+    result = await db.execute(
+        query.options(selectinload(Resource.uploader))
+        .order_by(Resource.created_at.desc())
+        .offset((page - 1) * page_size)
+        .limit(page_size)
+    )
+    resources = list(result.scalars().all())
+    return resources, total
+
+
+async def get_resource_by_id(db: AsyncSession, resource_id: int) -> Resource | None:
+    result = await db.execute(
+        select(Resource)
+        .options(selectinload(Resource.uploader))
+        .where(Resource.id == resource_id)
+    )
+    return result.scalar_one_or_none()
+
+
+async def increment_download_count(db: AsyncSession, resource: Resource) -> Resource:
+    resource.download_count += 1
+    await db.commit()
+    await db.refresh(resource)
+    return resource
+
+
+async def delete_resource(db: AsyncSession, resource: Resource):
+    await db.delete(resource)
+    await db.commit()
diff --git a/backend/app/services/schedule_service.py b/backend/app/services/schedule_service.py
index 44fa731..49a5f59 100644
--- a/backend/app/services/schedule_service.py
+++ b/backend/app/services/schedule_service.py
@@ -5,6 +5,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.db.models import Schedule
 from app.schemas.schedule import ScheduleCreate, ScheduleUpdate
+from app.services.notification_service import create_notifications_for_class
 
 
 async def create_schedule(
@@ -17,6 +18,13 @@ async def create_schedule(
     db.add(item)
     await db.commit()
     await db.refresh(item)
+
+    # Send notifications to class members
+    await create_notifications_for_class(
+        db, class_id, "schedule", f"新排期: {data.title}",
+        related_id=item.id,
+    )
+
     return item