byte[] fileStr=new  byte[5];

            MemoryStream btMs = new MemoryStream(fileStr);

            //以字符流的形式下载文件 

            byte[] bytes = new byte[(int)btMs.Length];

            btMs.Read(bytes, 0, bytes.Length);

            btMs.Close();

            Page.Response.ContentType = "application/octet-stream";

            //通知浏览器下载文件而不是打开

            Page.Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8));

            Page.Response.BinaryWrite(bytes);

            Page.Response.Flush();

            Page.Response.End();

public void Download(string path)

        {

            string filePath = HttpContext.Current.Server.MapPath(path);//路径

            //以字符流的形式下载文件

            FileStream fs = new FileStream(filePath, FileMode.Open);

            byte[] bytes = new byte[(int)fs.Length];

            fs.Read(bytes, 0, bytes.Length);

            fs.Close();

            HttpContext.Current.Response.ContentType = "application/octet-stream";

            HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode("test", System.Text.Encoding.UTF8));

            HttpContext.Current.Response.BinaryWrite(bytes);

            HttpContext.Current.Response.Flush();

            HttpContext.Current.Response.End();

        }