diff --git a/server/internal/repository/node_repository.go b/server/internal/repository/node_repository.go
index b497b26..c98c481 100644
--- a/server/internal/repository/node_repository.go
+++ b/server/internal/repository/node_repository.go
@@ -49,7 +49,20 @@ func (r *GormNodeRepository) FindByID(ctx context.Context, id uint) (*model.Node
 
 func (r *GormNodeRepository) FindByToken(ctx context.Context, token string) (*model.Node, error) {
 	var item model.Node
-	if err := r.db.WithContext(ctx).Where("token = ?", token).First(&item).Error; err != nil {
+	// 主 token 查询
+	err := r.db.WithContext(ctx).Where("token = ?", token).First(&item).Error
+	if err == nil {
+		return &item, nil
+	}
+	if !errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, err
+	}
+	// 回退：prev_token 且未过期
+	now := time.Now().UTC()
+	err = r.db.WithContext(ctx).
+		Where("prev_token = ? AND prev_token_expires IS NOT NULL AND prev_token_expires > ?", token, now).
+		First(&item).Error
+	if err != nil {
 		if errors.Is(err, gorm.ErrRecordNotFound) {
 			return nil, nil
 		}
diff --git a/server/internal/repository/node_repository_test.go b/server/internal/repository/node_repository_test.go
new file mode 100644
index 0000000..9c7ed2a
--- /dev/null
+++ b/server/internal/repository/node_repository_test.go
@@ -0,0 +1,76 @@
+package repository
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"backupx/server/internal/model"
+	"github.com/glebarez/sqlite"
+	"gorm.io/gorm"
+	gormlogger "gorm.io/gorm/logger"
+)
+
+func openTestNodeDB(t *testing.T) *gorm.DB {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "nodes.db")
+	db, err := gorm.Open(sqlite.Open(path), &gorm.Config{Logger: gormlogger.Default.LogMode(gormlogger.Silent)})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	if err := db.AutoMigrate(&model.Node{}); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+	return db
+}
+
+func TestFindByTokenFallsBackToPrevToken(t *testing.T) {
+	db := openTestNodeDB(t)
+	repo := NewNodeRepository(db)
+	ctx := context.Background()
+
+	future := time.Now().UTC().Add(24 * time.Hour)
+	node := &model.Node{
+		Name: "test", Token: "new-token",
+		PrevToken: "old-token", PrevTokenExpires: &future,
+	}
+	if err := repo.Create(ctx, node); err != nil {
+		t.Fatalf("create: %v", err)
+	}
+
+	// 新 token 能查到
+	got, err := repo.FindByToken(ctx, "new-token")
+	if err != nil || got == nil || got.ID != node.ID {
+		t.Fatalf("new token lookup failed: err=%v got=%v", err, got)
+	}
+
+	// 旧 token 也能查到（未过期）
+	got, err = repo.FindByToken(ctx, "old-token")
+	if err != nil || got == nil || got.ID != node.ID {
+		t.Fatalf("prev_token lookup failed: err=%v got=%v", err, got)
+	}
+}
+
+func TestFindByTokenRejectsExpiredPrevToken(t *testing.T) {
+	db := openTestNodeDB(t)
+	repo := NewNodeRepository(db)
+	ctx := context.Background()
+
+	past := time.Now().UTC().Add(-1 * time.Hour)
+	node := &model.Node{
+		Name: "test", Token: "new-token",
+		PrevToken: "stale", PrevTokenExpires: &past,
+	}
+	if err := repo.Create(ctx, node); err != nil {
+		t.Fatalf("create: %v", err)
+	}
+
+	got, err := repo.FindByToken(ctx, "stale")
+	if err != nil {
+		t.Fatalf("err=%v", err)
+	}
+	if got != nil {
+		t.Fatalf("expected stale prev_token rejected, got %v", got)
+	}
+}