diff --git a/app/database.py b/app/database.py
new file mode 100644
index 0000000..8d9f1eb
--- /dev/null
+++ b/app/database.py
@@ -0,0 +1,15 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker, declarative_base
+from .config import settings
+
+engine = create_engine(settings.database_url)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+Base = declarative_base()
+
+# 获取数据库连接的依赖项
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
\ No newline at end of file
diff --git a/app/main.py b/app/main.py
index ed51cae..66bec8f 100644
--- a/app/main.py
+++ b/app/main.py
@@ -1,58 +1,22 @@
 import uuid
-import boto3
 from fastapi import FastAPI, HTTPException, Depends
-from sqlalchemy import create_engine, Column, String, ForeignKey
-from sqlalchemy.orm import sessionmaker, Session, declarative_base, relationship
+from sqlalchemy.orm import Session
 
-from app.config import settings
-
-# --- 数据库初始化 ---
-engine = create_engine(settings.database_url)
-SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
-Base = declarative_base()
-
-# --- S3 客户端初始化 ---
-s3_client = boto3.client(
-    's3',
-    aws_access_key_id=settings.s3_access_key,
-    aws_secret_access_key=settings.s3_secret_key,
-    endpoint_url=settings.s3_endpoint,
-    region_name=settings.s3_region
-)
-
-# --- 数据模型 ---
-class Project(Base):
-    __tablename__ = "projects"
-    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
-    name = Column(String, nullable=False)
-    # cascade="all, delete-orphan" 确保在 db.delete(project) 时自动删除关联的 Markdown 记录
-    markdowns = relationship("Markdown", back_populates="project", cascade="all, delete-orphan")
-
-class Markdown(Base):
-    __tablename__ = "markdowns"
-    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
-    title = Column(String, nullable=False)
-    s3_key = Column(String, nullable=False)
-    project_id = Column(String, ForeignKey("projects.id", ondelete="CASCADE"))
-    project = relationship("Project", back_populates="markdowns")
+from .database import engine, Base, get_db
+from .models import Project, Markdown
+from .s3 import upload_to_s3, delete_from_s3
 
+# 启动时创建表
 Base.metadata.create_all(bind=engine)
 
-app = FastAPI()
-
-def get_db():
-    db = SessionLocal()
-    try:
-        yield db
-    finally:
-        db.close()
-
-# --- API 接口 ---
+app = FastAPI(title="AI Notion Backend")
 
 @app.get("/health")
 def health():
     return {"status": "ok"}
 
+# --- Project 接口 ---
+
 @app.post("/projects")
 def create_project(name: str, db: Session = Depends(get_db)):
     project = Project(name=name)
@@ -61,43 +25,40 @@ def create_project(name: str, db: Session = Depends(get_db)):
     db.refresh(project)
     return project
 
-@app.post("/projects/{project_id}/markdowns")
-def upload_markdown(project_id: str, title: str, content: str, db: Session = Depends(get_db)):
-    project = db.query(Project).filter(Project.id == project_id).first()
-    if not project:
-        raise HTTPException(status_code=404, detail="Project not found")
-    
-    # 1. 存入 S3
-    s3_key = f"projects/{project_id}/{uuid.uuid4()}.md"
-    s3_client.put_object(
-        Bucket=settings.s3_bucket_name,
-        Key=s3_key,
-        Body=content,
-        ContentType="text/markdown"
-    )
-
-    # 2. 存入数据库
-    md_record = Markdown(title=title, s3_key=s3_key, project_id=project_id)
-    db.add(md_record)
-    db.commit()
-    return {"id": md_record.id, "s3_key": s3_key}
-
 @app.delete("/projects/{project_id}")
 def delete_project(project_id: str, db: Session = Depends(get_db)):
     project = db.query(Project).filter(Project.id == project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     
-    # 1. 清理 S3 中的文件
-    markdowns = db.query(Markdown).filter(Markdown.project_id == project_id).all()
-    if markdowns:
-        keys = [{'Key': md.s3_key} for md in markdowns]
-        s3_client.delete_objects(
-            Bucket=settings.s3_bucket_name,
-            Delete={'Objects': keys}
-        )
+    # 1. 获取该项目下所有 Markdown 的 S3 keys 并从 S3 删除
+    s3_keys = [md.s3_key for md in project.markdowns]
+    delete_from_s3(s3_keys)
     
-    # 2. 从数据库删除项目 (SQLAlchemy 会自动处理 markdowns 表的级联删除)
+    # 2. 从数据库删除项目（SQLAlchemy 会自动级联删除对应的 Markdown 记录）
     db.delete(project)
     db.commit()
-    return {"message": f"Project {project_id} and its files have been purged."}
\ No newline at end of file
+    return {"message": f"Project {project_id} and associated files purged."}
+
+# --- Markdown 接口 ---
+
+@app.post("/projects/{project_id}/markdowns")
+def upload_markdown(project_id: str, title: str, content: str, db: Session = Depends(get_db)):
+    # 验证项目是否存在
+    project = db.query(Project).filter(Project.id == project_id).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+    
+    # 生成 S3 路径
+    s3_key = f"projects/{project_id}/{uuid.uuid4()}.md"
+    
+    # 1. 业务逻辑分离：上传 S3
+    upload_to_s3(s3_key, content)
+
+    # 2. 存入数据库记录
+    md_record = Markdown(title=title, s3_key=s3_key, project_id=project_id)
+    db.add(md_record)
+    db.commit()
+    db.refresh(md_record)
+    
+    return md_record
\ No newline at end of file
diff --git a/app/models.py b/app/models.py
new file mode 100644
index 0000000..6490ea7
--- /dev/null
+++ b/app/models.py
@@ -0,0 +1,19 @@
+import uuid
+from sqlalchemy import Column, String, ForeignKey
+from sqlalchemy.orm import relationship
+from .database import Base
+
+class Project(Base):
+    __tablename__ = "projects"
+    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
+    name = Column(String, nullable=False)
+    # 级联删除
+    markdowns = relationship("Markdown", back_populates="project", cascade="all, delete-orphan")
+
+class Markdown(Base):
+    __tablename__ = "markdowns"
+    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
+    title = Column(String, nullable=False)
+    s3_key = Column(String, nullable=False)
+    project_id = Column(String, ForeignKey("projects.id", ondelete="CASCADE"))
+    project = relationship("Project", back_populates="markdowns")
\ No newline at end of file
diff --git a/app/s3.py b/app/s3.py
new file mode 100644
index 0000000..575d573
--- /dev/null
+++ b/app/s3.py
@@ -0,0 +1,26 @@
+import boto3
+from .config import settings
+
+s3_client = boto3.client(
+    's3',
+    aws_access_key_id=settings.s3_access_key,
+    aws_secret_access_key=settings.s3_secret_key,
+    endpoint_url=settings.s3_endpoint,
+    region_name=settings.s3_region
+)
+
+def upload_to_s3(key: str, content: str):
+    s3_client.put_object(
+        Bucket=settings.s3_bucket_name,
+        Key=key,
+        Body=content,
+        ContentType="text/markdown"
+    )
+
+def delete_from_s3(keys: list[str]):
+    if not keys:
+        return
+    s3_client.delete_objects(
+        Bucket=settings.s3_bucket_name,
+        Delete={'Objects': [{'Key': k} for k in keys]}
+    )
\ No newline at end of file