diff --git a/services/user-service/internal/storage/mysql/user/common.go b/services/user-service/internal/storage/mysql/user/common.go
index 7841b458..4ca25add 100644
--- a/services/user-service/internal/storage/mysql/user/common.go
+++ b/services/user-service/internal/storage/mysql/user/common.go
@@ -222,6 +222,8 @@ func InsertUserIdentity(ctx context.Context, tx *sql.Tx, user userdomain.User, i
 		// 新用户默认短号永远是 default kind。
 		user.CurrentDisplayUserIDKind = userdomain.DisplayUserIDKindDefault
 	}
+	// profile_bg_img 是非空列；新建账号没有背景图时必须写空字符串，不能复用 NullableString 写成 SQL NULL。
+	profileBgImg := strings.TrimSpace(user.ProfileBgImg)
 
 	_, err := tx.ExecContext(ctx, `
 		INSERT INTO users (
@@ -265,7 +267,7 @@ func InsertUserIdentity(ctx context.Context, tx *sql.Tx, user userdomain.User, i
 			?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?,
 			?, ?, ?, ?, ?, ?
 		)
-	`, appcode.Normalize(user.AppCode), user.UserID, user.DefaultDisplayUserID, user.CurrentDisplayUserID, string(user.CurrentDisplayUserIDKind), shared.NullableString(user.Username), shared.NullableString(user.Gender), shared.NullableString(user.Country), shared.NullableRegionID(user.RegionID), shared.NullableString(user.InviteCode), shared.NullableString(user.RegisterIP), shared.NullableString(user.RegisterUserAgent), shared.NullableString(user.CountryByIP), shared.NullableString(user.RegisterDeviceID), shared.NullableString(user.RegisterDevice), shared.NullableString(user.RegisterOSVersion), shared.NullableString(user.Avatar), shared.NullableString(user.ProfileBgImg), shared.NullableString(user.BirthDate), shared.NullableString(user.RegisterAppVersion), shared.NullableString(user.RegisterBuildNumber), shared.NullableString(user.RegisterSource), shared.NullableString(user.RegisterInstallChannel), shared.NullableString(user.RegisterCampaign), shared.NullableString(user.RegisterPlatform), shared.NullableString(user.Language), shared.NullableString(user.Timezone), user.ProfileCompleted, user.ProfileCompletedAtMs, onboardingStatusForInsert(user), string(user.Status), user.CreatedAtMs, user.UpdatedAtMs)
+	`, appcode.Normalize(user.AppCode), user.UserID, user.DefaultDisplayUserID, user.CurrentDisplayUserID, string(user.CurrentDisplayUserIDKind), shared.NullableString(user.Username), shared.NullableString(user.Gender), shared.NullableString(user.Country), shared.NullableRegionID(user.RegionID), shared.NullableString(user.InviteCode), shared.NullableString(user.RegisterIP), shared.NullableString(user.RegisterUserAgent), shared.NullableString(user.CountryByIP), shared.NullableString(user.RegisterDeviceID), shared.NullableString(user.RegisterDevice), shared.NullableString(user.RegisterOSVersion), shared.NullableString(user.Avatar), profileBgImg, shared.NullableString(user.BirthDate), shared.NullableString(user.RegisterAppVersion), shared.NullableString(user.RegisterBuildNumber), shared.NullableString(user.RegisterSource), shared.NullableString(user.RegisterInstallChannel), shared.NullableString(user.RegisterCampaign), shared.NullableString(user.RegisterPlatform), shared.NullableString(user.Language), shared.NullableString(user.Timezone), user.ProfileCompleted, user.ProfileCompletedAtMs, onboardingStatusForInsert(user), string(user.Status), user.CreatedAtMs, user.UpdatedAtMs)
 	if err != nil {
 		return err
 	}