JS代码 

$().ready(function () {
        $("#file").change(function () {
            $("#filename").val($(this).val());
        });

                $("#btn").click(function () {
                    $.ajaxFileUpload({
                        secureuri: false,
                        fileElementId: "file",
                        dataType: "json",
                        url: "Upload",
                        success: function (data, status) {
                            if (typeof (data.error) != 'undefined') {
                                if (data.error != '') {
                                    alert(data.error);
                                } else {
                                    alert(data.msg);
                                }
                            }
                        },
                        error: function (data, status, e) {
                            alert("上传失败");
                            alert(e);
                        }
                    });
                });

HTML代码
<img src="../../../../Content/images/loading.gif" id="loading" style="display:none;" />
    <input type="text" id="filename" name="filename" value="" />
    <input type="file" id="file" name="file" value="" style="width:65px;"/>
    <input type="button" value="上传" id="btn" >