var options = {
        dataType: 'json',
        beforeSubmit: _this.showRequest,  //提交前处理
        error: _this.showError,           //错误处理
        success: _this.showResponse       //提交成功的处理
    };
    $("#myForm").ajaxForm(options);

------解决方案--------------------


纯ajax没有办法执行文件上传

你要上传文件必须有一个隐藏的frame 通过这个子frame上传 然后向子写入js代码来通知页面

前台的代码：
HTML code

<div id="UpLoad_Show">

</div>

<script type="text/javascript">
    function UpLoadPictureShow(id, ifVertically) {
        var value = $("#pictures").val();
        var img;
        if (ifVertically == "Vertically") {
            img = "<img alt='' src='/File/DownLoad/" + id + "' width='90px' height='120px' />&nbsp;";
        }
        else {
            img = "<img alt='' src='/File/DownLoad/" + id + "' width='120px' height='90px' />&nbsp;";
        }
        $("#UpLoad_Show").append(img);
        if (value == 0) {
            value = id;
        }
        else {
            value += "," + id;
        }
        $("#pictures").val(value);
    }
</script>

<div>
    <form action="/File/UpLoadPicture" method="post" enctype="multipart/form-data" target="UpLoad_Do">
        <input name="File1" type="file" />
        <input type="submit" value="上传" />
    </form>
    <iframe id="UpLoad_Do" src="../Child/UpLoad.htm" style="display:none"></iframe>
</div>