diff --git a/backend/services/identity-service/src/domain/aggregates/user-account/user-account.aggregate.ts b/backend/services/identity-service/src/domain/aggregates/user-account/user-account.aggregate.ts
index 6da2fa17..dd379b0a 100644
--- a/backend/services/identity-service/src/domain/aggregates/user-account/user-account.aggregate.ts
+++ b/backend/services/identity-service/src/domain/aggregates/user-account/user-account.aggregate.ts
@@ -96,8 +96,9 @@ export class UserAccount {
       params.initialDeviceId, params.deviceName || '未命名设备', new Date(), new Date(),
     ));
 
+    // UserID将由数据库自动生成(autoincrement)，这里使用临时值0
     const account = new UserAccount(
-      UserId.generate(), params.accountSequence, devices, null,
+      UserId.create(0), params.accountSequence, devices, null,
       `用户${params.accountSequence.value}`, null, params.inviterSequence,
       ReferralCode.generate(), params.province, params.city, null,
       new Map(), null, KYCStatus.NOT_VERIFIED, AccountStatus.ACTIVE,
diff --git a/backend/services/identity-service/src/domain/value-objects/index.ts b/backend/services/identity-service/src/domain/value-objects/index.ts
index a3800b80..c078980e 100644
--- a/backend/services/identity-service/src/domain/value-objects/index.ts
+++ b/backend/services/identity-service/src/domain/value-objects/index.ts
@@ -5,21 +5,27 @@ import { wordlist } from '@scure/bip39/wordlists/english';
 
 // ============ UserId ============
 export class UserId {
-  constructor(public readonly value: string) {
+  constructor(public readonly value: bigint) {
     if (!value) throw new DomainError('UserId不能为空');
   }
 
-  static generate(): UserId {
-    return new UserId(crypto.randomUUID());
-  }
-
-  static create(value: string): UserId {
+  static create(value: bigint | string | number): UserId {
+    if (typeof value === 'string') {
+      return new UserId(BigInt(value));
+    }
+    if (typeof value === 'number') {
+      return new UserId(BigInt(value));
+    }
     return new UserId(value);
   }
 
   equals(other: UserId): boolean {
     return this.value === other.value;
   }
+
+  toString(): string {
+    return this.value.toString();
+  }
 }
 
 // ============ AccountSequence ============
diff --git a/backend/services/identity-service/src/infrastructure/persistence/repositories/user-account.repository.impl.ts b/backend/services/identity-service/src/infrastructure/persistence/repositories/user-account.repository.impl.ts
index f02341ca..27920fea 100644
--- a/backend/services/identity-service/src/infrastructure/persistence/repositories/user-account.repository.impl.ts
+++ b/backend/services/identity-service/src/infrastructure/persistence/repositories/user-account.repository.impl.ts
@@ -14,54 +14,66 @@ export class UserAccountRepositoryImpl implements UserAccountRepository {
 
   async save(account: UserAccount): Promise<void> {
     const devices = account.getAllDevices();
-    const wallets = account.getAllWalletAddresses();
+    const isNewAccount = account.userId.value === BigInt(0);
 
     await this.prisma.$transaction(async (tx) => {
-      await tx.userAccount.upsert({
-        where: { userId: BigInt(account.userId.value) },
-        create: {
-          userId: BigInt(account.userId.value),
-          accountSequence: BigInt(account.accountSequence.value),
-          phoneNumber: account.phoneNumber?.value || null,
-          nickname: account.nickname,
-          avatarUrl: account.avatarUrl,
-          inviterSequence: account.inviterSequence ? BigInt(account.inviterSequence.value) : null,
-          referralCode: account.referralCode.value,
-          provinceCode: account.province.value,
-          cityCode: account.city.value,
-          address: account.addressDetail,
-          kycStatus: account.kycStatus,
-          realName: account.kycInfo?.realName || null,
-          idCardNumber: account.kycInfo?.idCardNumber || null,
-          idCardFrontUrl: account.kycInfo?.idCardFrontUrl || null,
-          idCardBackUrl: account.kycInfo?.idCardBackUrl || null,
-          status: account.status,
-          registeredAt: account.registeredAt,
-          lastLoginAt: account.lastLoginAt,
-        },
-        update: {
-          phoneNumber: account.phoneNumber?.value || null,
-          nickname: account.nickname,
-          avatarUrl: account.avatarUrl,
-          provinceCode: account.province.value,
-          cityCode: account.city.value,
-          address: account.addressDetail,
-          kycStatus: account.kycStatus,
-          realName: account.kycInfo?.realName || null,
-          idCardNumber: account.kycInfo?.idCardNumber || null,
-          idCardFrontUrl: account.kycInfo?.idCardFrontUrl || null,
-          idCardBackUrl: account.kycInfo?.idCardBackUrl || null,
-          status: account.status,
-          lastLoginAt: account.lastLoginAt,
-        },
-      });
+      let savedUserId: bigint;
+
+      if (isNewAccount) {
+        // 新账户，让数据库自动生成userId
+        const created = await tx.userAccount.create({
+          data: {
+            accountSequence: BigInt(account.accountSequence.value),
+            phoneNumber: account.phoneNumber?.value || null,
+            nickname: account.nickname,
+            avatarUrl: account.avatarUrl,
+            inviterSequence: account.inviterSequence ? BigInt(account.inviterSequence.value) : null,
+            referralCode: account.referralCode.value,
+            provinceCode: account.province.value,
+            cityCode: account.city.value,
+            address: account.addressDetail,
+            kycStatus: account.kycStatus,
+            realName: account.kycInfo?.realName || null,
+            idCardNumber: account.kycInfo?.idCardNumber || null,
+            idCardFrontUrl: account.kycInfo?.idCardFrontUrl || null,
+            idCardBackUrl: account.kycInfo?.idCardBackUrl || null,
+            status: account.status,
+            registeredAt: account.registeredAt,
+            lastLoginAt: account.lastLoginAt,
+          },
+        });
+        savedUserId = created.userId;
+        // 更新聚合根的userId
+        (account as any)._userId = UserId.create(savedUserId);
+      } else {
+        // 已存在的账户，更新
+        await tx.userAccount.update({
+          where: { userId: BigInt(account.userId.value) },
+          data: {
+            phoneNumber: account.phoneNumber?.value || null,
+            nickname: account.nickname,
+            avatarUrl: account.avatarUrl,
+            provinceCode: account.province.value,
+            cityCode: account.city.value,
+            address: account.addressDetail,
+            kycStatus: account.kycStatus,
+            realName: account.kycInfo?.realName || null,
+            idCardNumber: account.kycInfo?.idCardNumber || null,
+            idCardFrontUrl: account.kycInfo?.idCardFrontUrl || null,
+            idCardBackUrl: account.kycInfo?.idCardBackUrl || null,
+            status: account.status,
+            lastLoginAt: account.lastLoginAt,
+          },
+        });
+        savedUserId = account.userId.value;
+      }
 
       // Sync devices
-      await tx.userDevice.deleteMany({ where: { userId: BigInt(account.userId.value) } });
+      await tx.userDevice.deleteMany({ where: { userId: savedUserId } });
       if (devices.length > 0) {
         await tx.userDevice.createMany({
           data: devices.map((d) => ({
-            userId: BigInt(account.userId.value),
+            userId: savedUserId,
             deviceId: d.deviceId,
             deviceName: d.deviceName,
             addedAt: d.addedAt,