请问能直接用as3直传OSS么？

如题，求助。。
flash的as3，用 FileReference 类的 upload() 方法来上传，但捣鼓了半天一直不成功。。
感觉js能直传，as3也应该可以。。


as3的上传主要代码如下：
// 注：以下部分值用的假数据

var host:String = "http://test-001.oss-cn-shenzhen.aliyuncs.com";
var request:URLRequest = new URLRequest(host);
var params:URLVariables = new URLVariables();
params.OSSAccessKeyId = "RVDIwmBHpBrtyOIm"; // 注：这里用的假数据
params.key = "1.jpg";
params.signature = "ldrtbWJT5hAwJ4tYLWRljOvBes8=";
params.policy = "ayJleHBphyF0aW9uIjoiMjAyMC0wMS0wMVQxMjowMDowMC4wMDBaIir4Y29uZGl0aW9ucyI6W1siY29udGVudC1sZW5ndGewqkFuZ2UiLDAsMTA0ODU3NjAwFeF3MF1dfP==";
request.method = URLRequestMethod.POST;
request.data = params;

fileReference.addEventListener(ProgressEvent.PROGRESS, evtUploadProgress);
fileReference.addEventListener(DataEvent.UPLOAD_COMPLETE_DATA, evtUploadEnd1);
fileReference.addEventListener(IOErrorEvent.IO_ERROR, evtIOError);
fileReference.upload(request);
然后收到返回：



<?xml version="1.0" encoding="UTF-8"?>
<Error>
  <Code>IncorrectNumberOfFilesInPOSTRequest</Code>
  <Message>POST requires exactly one file upload per request.</Message>
  <RequestId>58BD32A277F1382FD2A85874</RequestId>
  <HostId>zy-test-001.oss-cn-shenzhen.aliyuncs.com</HostId>
</Error>


求指点指点~~~~~