string fileName = filename;
                string filePath = Server.MapPath(ResolveUrl("~/DataBackUp/")) + filename;//路径
                FileStream fs = new FileStream(filePath, FileMode.Open);
                byte[] bytes = new byte[(int)fs.Length];
                fs.Read(bytes, 0, bytes.Length);
                fs.Close();
                Response.ContentType = "application/octet-stream";
                Response.AddHeader("Content-Disposition", "attachment; filename=" +fileName);
                Response.BinaryWrite(bytes);
                Response.Flush();
                Response.End();