服务端test.php

if (isset($_POST['upload'])) {
  var_dump($_FILES);
  move_uploaded_file($_FILES['upfile']['tmp_name'], 'up_tmp/'.time().'.dat');
  //header('location: test.php');
  exit;
}

上传端index.html 

<!doctype html>
<html lang="zh">
<head>
<meta charset="utf-8">
<title>HTML5 Ajax Uploader</title>
<script src="jquery-2.1.1.min.js"></script>
</head>
<body>
<p><input type="file" id="upfile"></p>
<p><input type="button" id="upJS" value="用原生JS上传"></p>
<p><input type="button" id="upJQuery" value="用jQuery上传"></p>
<script>
  /*原生JS版*/
  document.getElementById("upJS").onclick = function() {
    /* FormData 是表单数据类 */
    var fd = new FormData();
    var ajax = new XMLHttpRequest();
    fd.append("upload", 1);
    /* 把文件添加到表单里 */
    fd.append("upfile", document.getElementById("upfile").files[0]);
    ajax.open("post", "test.php", true);
    ajax.onload = function () {
      console.log(ajax.responseText);
    };
    ajax.send(fd);
  }
  /* jQuery 版 */
  $('#upJQuery').on('click', function() {
    var fd = new FormData();
    fd.append("upload", 1);
    fd.append("upfile", $("#upfile").get(0).files[0]);
    $.ajax({
      url: "test.php",
      type: "POST",
      processData: false,
      contentType: false,
      data: fd,
      success: function(d) {
        console.log(d);
      }
    });
  });
</script>
</body>
</html>