diff --git a/backend/src/controllers/authController.js b/backend/src/controllers/authController.js
index 591ad41..2d9df9f 100644
--- a/backend/src/controllers/authController.js
+++ b/backend/src/controllers/authController.js
@@ -26,6 +26,11 @@ const wechatLogin = async (req, res) => {
 
     const { code, userInfo, invitationCode } = req.body;
 
+    console.log('=== WeChat Login Request ===');
+    console.log('Code:', code);
+    console.log('InvitationCode:', invitationCode);
+    console.log('UserInfo:', userInfo);
+
     // Extract device info from request
     const deviceInfo = {
       ipAddress: req.ip || req.connection.remoteAddress,
@@ -41,6 +46,10 @@ const wechatLogin = async (req, res) => {
       deviceInfo
     );
 
+    console.log('=== Login Result ===');
+    console.log('User ID:', result.user.id);
+    console.log('User invitedBy:', result.user.invitedBy);
+
     return sendSuccess(res, {
       user: {
         id: result.user.id,
diff --git a/backend/src/services/authService.js b/backend/src/services/authService.js
index b7b44af..70c274c 100644
--- a/backend/src/services/authService.js
+++ b/backend/src/services/authService.js
@@ -89,6 +89,10 @@ const wechatLogin = async (code, userInfo = {}, invitationCode = null, deviceInf
       console.error('Failed to get default avatar config:', e);
     }
 
+    console.log('=== Creating New User ===');
+    console.log('OpenId:', openId);
+    console.log('InvitationCode received:', invitationCode);
+
     // Create new user
     const userData = {
       wechatOpenId: openId,
@@ -100,14 +104,18 @@ const wechatLogin = async (code, userInfo = {}, invitationCode = null, deviceInf
     // Handle invitation
     let inviterId = null;
     if (invitationCode) {
+      console.log('Looking for inviter with code:', invitationCode);
       const inviter = await User.findOne({ where: { invitationCode } });
+      console.log('Inviter found:', inviter ? inviter.id : 'NOT FOUND');
       if (inviter) {
         userData.invitedBy = inviter.id;
         inviterId = inviter.id;
+        console.log('Setting invitedBy to:', inviter.id);
       }
     }
 
     user = await User.create(userData);
+    console.log('New user created:', user.id, 'invitedBy:', user.invitedBy);
 
     // Record invitation relationship
     if (inviterId) {
@@ -118,11 +126,33 @@ const wechatLogin = async (code, userInfo = {}, invitationCode = null, deviceInf
         registeredAt: new Date(),
         rewardStatus: 'pending',
       });
+      console.log('Invitation record created');
     }
   } else {
     // Update existing user info if provided
     if (userInfo.nickname) user.nickname = userInfo.nickname;
     if (userInfo.avatar) user.avatar = userInfo.avatar;
+    
+    // Handle invitation for existing user who hasn't been invited yet
+    if (invitationCode && !user.invitedBy) {
+      const inviter = await User.findOne({ where: { invitationCode } });
+      if (inviter && inviter.id !== user.id) {
+        // Bind invitation relationship
+        user.invitedBy = inviter.id;
+        
+        // Record invitation relationship
+        await Invitation.create({
+          inviterId: inviter.id,
+          inviteeId: user.id,
+          invitationCode,
+          registeredAt: new Date(),
+          rewardStatus: 'pending',
+        });
+        
+        console.log(`User ${user.id} bound to inviter ${inviter.id} via code ${invitationCode}`);
+      }
+    }
+    
     await user.save();
   }