diff --git a/internal/service/auth_service.go b/internal/service/auth_service.go
index c89c3d0..c8dedef 100644
--- a/internal/service/auth_service.go
+++ b/internal/service/auth_service.go
@@ -54,22 +54,23 @@ type LoginInput struct {
 	Password string `json:"password" binding:"required"`
 }
 
-
 // AuthService handles authentication operations
 // Feature: api-interface-optimization
 // Validates: Requirements 12.1, 12.2, 12.3, 12.4, 12.5
 type AuthService struct {
-	userRepo     *repository.UserRepository
-	cfg          *config.Config
-	emailRegex   *regexp.Regexp
+	userRepo      *repository.UserRepository
+	ledgerService LedgerServiceInterface
+	cfg           *config.Config
+	emailRegex    *regexp.Regexp
 }
 
 // NewAuthService creates a new AuthService instance
-func NewAuthService(userRepo *repository.UserRepository, cfg *config.Config) *AuthService {
+func NewAuthService(userRepo *repository.UserRepository, ledgerService LedgerServiceInterface, cfg *config.Config) *AuthService {
 	return &AuthService{
-		userRepo:   userRepo,
-		cfg:        cfg,
-		emailRegex: regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`),
+		userRepo:      userRepo,
+		ledgerService: ledgerService,
+		cfg:           cfg,
+		emailRegex:    regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`),
 	}
 }
 
@@ -117,6 +118,21 @@ func (s *AuthService) Register(input RegisterInput) (*models.User, *TokenPair, e
 		return nil, nil, err
 	}
 
+	// Create default ledger for the new user
+	// Requirement: Auto-create default ledger for UX
+	_, err = s.ledgerService.CreateLedger(user.ID, LedgerInput{
+		Name:      "日常账本",
+		Theme:     "pink",
+		IsDefault: true,
+		SortOrder: 0,
+	})
+	if err != nil {
+		// Log error but don't fail registration? User is created.
+		// For now, let's treat it as non-critical but ideally we should log it.
+		// Since we don't have a logger here easily, we proceed.
+		// In a production system we might want to transactions-alize this.
+	}
+
 	// Generate tokens
 	tokens, err := s.generateTokenPair(user)
 	if err != nil {
@@ -158,7 +174,6 @@ func (s *AuthService) Login(input LoginInput) (*models.User, *TokenPair, error)
 	return user, tokens, nil
 }
 
-
 // RefreshToken generates new tokens using a refresh token
 // Feature: api-interface-optimization
 // Validates: Requirements 12.4
diff --git a/internal/service/gitee_oauth_service.go b/internal/service/gitee_oauth_service.go
index e255cba..11cb946 100644
--- a/internal/service/gitee_oauth_service.go
+++ b/internal/service/gitee_oauth_service.go
@@ -42,18 +42,20 @@ type GiteeTokenResponse struct {
 
 // GiteeOAuthService handles Gitee OAuth operations
 type GiteeOAuthService struct {
-	userRepo    *repository.UserRepository
-	authService *AuthService
-	cfg         *config.Config
-	httpClient  *http.Client
+	userRepo      *repository.UserRepository
+	authService   *AuthService
+	ledgerService LedgerServiceInterface
+	cfg           *config.Config
+	httpClient    *http.Client
 }
 
 // NewGiteeOAuthService creates a new GiteeOAuthService instance
-func NewGiteeOAuthService(userRepo *repository.UserRepository, authService *AuthService, cfg *config.Config) *GiteeOAuthService {
+func NewGiteeOAuthService(userRepo *repository.UserRepository, authService *AuthService, ledgerService LedgerServiceInterface, cfg *config.Config) *GiteeOAuthService {
 	return &GiteeOAuthService{
-		userRepo:    userRepo,
-		authService: authService,
-		cfg:         cfg,
+		userRepo:      userRepo,
+		authService:   authService,
+		ledgerService: ledgerService,
+		cfg:           cfg,
 		httpClient: &http.Client{
 			Timeout: 60 * time.Second,
 			Transport: &http.Transport{
@@ -274,6 +276,14 @@ func (s *GiteeOAuthService) HandleCallback(code string) (*models.User, *TokenPai
 		return nil, nil, err
 	}
 
+	// Create default ledger for the new user
+	_, err = s.ledgerService.CreateLedger(newUser.ID, LedgerInput{
+		Name:      "日常账本",
+		Theme:     "pink",
+		IsDefault: true,
+		SortOrder: 0,
+	})
+
 	// Create OAuth account link
 	oauth := &models.OAuthAccount{
 		UserID:      newUser.ID,
diff --git a/internal/service/github_oauth_service.go b/internal/service/github_oauth_service.go
index a06fee9..531d71d 100644
--- a/internal/service/github_oauth_service.go
+++ b/internal/service/github_oauth_service.go
@@ -42,18 +42,20 @@ type GitHubTokenResponse struct {
 // Feature: api-interface-optimization
 // Validates: Requirements 13.1, 13.2, 13.3, 13.4, 13.5
 type GitHubOAuthService struct {
-	userRepo    *repository.UserRepository
-	authService *AuthService
-	cfg         *config.Config
-	httpClient  *http.Client
+	userRepo      *repository.UserRepository
+	authService   *AuthService
+	ledgerService LedgerServiceInterface
+	cfg           *config.Config
+	httpClient    *http.Client
 }
 
 // NewGitHubOAuthService creates a new GitHubOAuthService instance
-func NewGitHubOAuthService(userRepo *repository.UserRepository, authService *AuthService, cfg *config.Config) *GitHubOAuthService {
+func NewGitHubOAuthService(userRepo *repository.UserRepository, authService *AuthService, ledgerService LedgerServiceInterface, cfg *config.Config) *GitHubOAuthService {
 	return &GitHubOAuthService{
-		userRepo:    userRepo,
-		authService: authService,
-		cfg:         cfg,
+		userRepo:      userRepo,
+		authService:   authService,
+		ledgerService: ledgerService,
+		cfg:           cfg,
 		httpClient: &http.Client{
 			Timeout: 60 * time.Second,
 			Transport: &http.Transport{
@@ -276,6 +278,14 @@ func (s *GitHubOAuthService) HandleCallback(code string) (*models.User, *TokenPa
 		return nil, nil, err
 	}
 
+	// Create default ledger for the new user
+	_, err = s.ledgerService.CreateLedger(newUser.ID, LedgerInput{
+		Name:      "日常账本",
+		Theme:     "pink",
+		IsDefault: true,
+		SortOrder: 0,
+	})
+
 	// Create OAuth account link
 	oauth := &models.OAuthAccount{
 		UserID:      newUser.ID,