private void DownLoadFile(string fileName)
    {
        if (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(fileName)))
        {
            System.Web.HttpContext.Current.Response.ClearHeaders();
            string showName = System.Web.HttpUtility.UrlEncode(System.Text.Encoding.UTF8.GetBytes(fileName));//转换成显示文件名
            System.Web.HttpContext.Current.Response.ContentType = "application/zip;";
            System.Web.HttpContext.Current.Response.Charset = "UTF-8";
            System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", string.Format("attachment;filename=\"{0}\"", showName));
            System.Web.HttpContext.Current.Response.BinaryWrite(GetFileBytes(fileName));
            System.Web.HttpContext.Current.Response.End();
        }
    }
    private byte[] GetFileBytes(string fileName)
    {
        try
        {
            System.IO.FileStream fileStream = new System.IO.FileStream(System.Web.HttpContext.Current.Server.MapPath(fileName), System.IO.FileMode.Open, System.IO.FileAccess.Read);
            byte[] bytes = new byte[fileStream.Length];
            fileStream.Read(bytes, 0, (int)fileStream.Length);
            return bytes;
        }
        catch
        {
            return null;
        }
    }