我不能用异步Ajax上传文件，那么可以使用同步方法吗？我搜索了一下，却一无所获。
谢谢！
No. You need to upload through a regular form. The only "ajax" upload plugins I've seen create an iframe dynamically through javascript and reconstruct the form in it and submit it through the iframe like your browser would normally.
No, you can not with pure Ajax. However, there are many hidden IFRAME based solutions that mimic the exact behavior. Here is one example: http://www.openjs.com/articles/ajax/ajax_file_upload/
UPDATE
Here is another implemented as a jQuery plugin: http://www.phpletter.com/Demo/AjaxFileUpload-Demo/
For asynchronous fileupload, try something like uploadify