diff --git a/client.go b/client.go
index 3520fbc..764911b 100644
--- a/client.go
+++ b/client.go
@@ -30,11 +30,12 @@ const (
 //   - NewBearerClient:  管理端（使用已有的 Bearer Token）
 //   - NewUserTokenClient: 发送端（X-SMS-Token + 请求签名，仅可调用发送接口）
 type Client struct {
-	baseURL    string
-	mode       authMode
-	bearer     string
-	userToken  string
-	httpClient *http.Client
+	baseURL      string
+	mode         authMode
+	bearer       string
+	serviceToken string
+	userToken    string
+	httpClient   *http.Client
 }
 
 // Option 用于在构造 Client 时传入可选配置。
@@ -65,6 +66,7 @@ func NewServiceClient(baseURL, serviceToken string, opts ...Option) (*Client, er
 		o(c)
 	}
 
+	c.serviceToken = serviceToken
 	token, err := c.serviceTokenLogin(context.Background(), serviceToken)
 	if err != nil {
 		return nil, fmt.Errorf("service token login: %w", err)
@@ -197,6 +199,10 @@ func structToMap(v interface{}) (map[string]interface{}, error) {
 }
 
 func doRequest[T any](c *Client, ctx context.Context, method, path string, body interface{}, query url.Values) (T, error) {
+	return doRequestRetry[T](c, ctx, method, path, body, query, false)
+}
+
+func doRequestRetry[T any](c *Client, ctx context.Context, method, path string, body interface{}, query url.Values, retried bool) (T, error) {
 	var zero T
 
 	var bodyReader io.Reader
@@ -252,6 +258,15 @@ func doRequest[T any](c *Client, ctx context.Context, method, path string, body
 		return zero, fmt.Errorf("unmarshal response (status %d): %w\nbody: %s", resp.StatusCode, err, string(respBody))
 	}
 
+	if apiResp.Code == 401 && c.serviceToken != "" && !retried {
+		newToken, loginErr := c.serviceTokenLogin(ctx, c.serviceToken)
+		if loginErr != nil {
+			return zero, &APIError{Code: 401, Message: apiResp.Message}
+		}
+		c.bearer = newToken
+		return doRequestRetry[T](c, ctx, method, path, body, query, true)
+	}
+
 	if apiResp.Code != 200 {
 		return zero, &APIError{Code: apiResp.Code, Message: apiResp.Message}
 	}