diff --git a/internal/common/auth/service/auth_service.go b/internal/common/auth/service/auth_service.go
index 16e341d..e135d2c 100644
--- a/internal/common/auth/service/auth_service.go
+++ b/internal/common/auth/service/auth_service.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"strings"
 	"sync"
 
 	"wx_service/internal/model"
@@ -17,6 +18,8 @@ var (
 	ErrMiniProgramNotFound = errors.New("mini program not found")
 )
 
+const defaultAvatarURL = "https://linghu-wmr.oss-cn-beijing.aliyuncs.com/smt/avatar.png"
+
 type AuthService struct {
 	db                *gorm.DB
 	miniProgramSvc    *MiniProgramService
@@ -72,6 +75,8 @@ func (s *AuthService) LoginWithCode(ctx context.Context, req LoginRequest) (*Log
 		return nil, fmt.Errorf("wechat response missing openid")
 	}
 
+	avatarURL := normalizeAvatarURL(req.AvatarURL)
+
 	tx := s.db.WithContext(ctx)
 	var user model.User
 	err = tx.Where("mini_program_id = ? AND open_id = ?", miniProgram.ID, session.OpenID).First(&user).Error
@@ -81,7 +86,7 @@ func (s *AuthService) LoginWithCode(ctx context.Context, req LoginRequest) (*Log
 			OpenID:        session.OpenID,
 			UnionID:       session.UnionID,
 			NickName:      req.NickName,
-			AvatarURL:     req.AvatarURL,
+			AvatarURL:     avatarURL,
 			Phone:         req.Phone,
 			SessionKey:    session.SessionKey,
 		}
@@ -105,9 +110,13 @@ func (s *AuthService) LoginWithCode(ctx context.Context, req LoginRequest) (*Log
 			updates["nick_name"] = req.NickName
 			user.NickName = req.NickName
 		}
-		if req.AvatarURL != "" && req.AvatarURL != user.AvatarURL {
-			updates["avatar_url"] = req.AvatarURL
-			user.AvatarURL = req.AvatarURL
+		if req.AvatarURL != "" && avatarURL != user.AvatarURL {
+			updates["avatar_url"] = avatarURL
+			user.AvatarURL = avatarURL
+		}
+		if strings.TrimSpace(user.AvatarURL) == "" {
+			updates["avatar_url"] = defaultAvatarURL
+			user.AvatarURL = defaultAvatarURL
 		}
 		if req.Phone != "" && req.Phone != user.Phone {
 			updates["phone"] = req.Phone
@@ -147,3 +156,11 @@ func (s *AuthService) getWeChatClient(mp *model.MiniProgram) *WeChatClient {
 	s.cacheMu.Unlock()
 	return newClient
 }
+
+func normalizeAvatarURL(raw string) string {
+	text := strings.TrimSpace(raw)
+	if text == "" {
+		return defaultAvatarURL
+	}
+	return text
+}