<script src="/Content/JQueryJS/jquery-2.1.1.js"></script>
<script src="/Content/Js/ajaxfileupload.js"></script>

 <input id="fileToUpload" type="file" name="fileToUpload">

function saveCInfo() {
            var filename = document.getElementById("fileToUpload").value;
            if (filename != "") {
                $.ajaxFileUpload({
                    url: '../Order/OrderExec.ashx?oprMode=fileUpload' + "&filename=" + filename + "&billno=" + billno + "&companyname=" + companyname,
                    secureuri: false,
                    fileElementId: 'fileToUpload',//上傳控件ID
                    //dataType: 'json',
                    error: function () { alert('error'); },
                    success: function (datax) {
                        if (datax != "") {
                            msgShow('系統提示', '上傳成功!', 'info');
                        } else {
                            msgShow('系統提示', '上傳失敗!', 'info');
                        }
                    }
                });
            } else {
                $.messager.alert('提示', '請選擇上傳文件', 'info');
            }
        }

public void FileUpload(HttpContext context)
        {
            try
            {
                context.Response.ContentType = "text/html";
                string companyname = context.Request.Params["companyname"];
                string billno = context.Request.Params["billno"];
                string filename = context.Request.Params["filename"];
                string name = companyname + "_" + billno + "_" + filename;
                HttpFileCollection files = HttpContext.Current.Request.Files;
                //指定上傳文件在服務器上的保存路徑
                string savePath = context.Server.MapPath("~/upload/");
                //檢查服務器上是否存在這個物理路徑，如果不存在則創建
                if (!System.IO.Directory.Exists(savePath))
                {
                    System.IO.Directory.CreateDirectory(savePath);
                }
                savePath = savePath + name;//上傳文件路徑
                files[0].SaveAs(savePath);//保存文件
                context.Response.Write(savePath);
            }
            catch (Exception ex)
            {
                context.Response.Write("FileUpload: " + ex.Message);
            }

        }