diff --git a/tests/test-ufile.py b/tests/test-ufile.py
index 7ef881b..6fc9165 100644
--- a/tests/test-ufile.py
+++ b/tests/test-ufile.py
@@ -35,7 +35,7 @@
 AUTHORIZATION = "UCloud public-key:vex1mk5WI2fe/i5TzXm7QY19p64="
 PARAMS = dict(
     UCloudPublicKey="public-key",
-    Signature="JHrQ1u087Gv0ktLlBAyfYclnI/I=",
+    Signature="i85wNCWK1eotra5GWAF9WfHfjsY=",
     Expires="1"
 )
 
diff --git a/ucloudauth/ufile.py b/ucloudauth/ufile.py
index 9744494..da23915 100644
--- a/ucloudauth/ufile.py
+++ b/ucloudauth/ufile.py
@@ -123,7 +123,7 @@ def gen_str_to_sign(self, req):
         str_to_sign = "\n".join([
             req.method,
             req.headers.get("content-md5", ""),
-            req.headers["content-type"],
+            req.headers.get("content-type", ""),
             req.headers.get("date", self._expires),
             canonicalized_headers + canonicalized_resource
         ])
@@ -137,7 +137,9 @@ def fill_all_headers(self, req):
         if content_type is None:
             content_type = self.DEFAULT_TYPE
             logger.warn("can not determine mime-type for {0}".format(url.path))
-        req.headers.setdefault("content-type", content_type)
+        if self._expires is None:
+            # sign with url, no content-type for url
+            req.headers.setdefault("content-type", content_type)
 
         if (
             req.body is not None