var fd = new FormData(document.getElementById("fileinfo")); fd.append("CustomField", "This is some extra data"); $.ajax({ url: "stash.php", type: "POST", data: fd, processData: false, // 告诉 jQuery 不要去处理发送的数据 contentType: false // 告诉 jQuery 不要去设置 Content-Type 请求头 });