public static void SaveQrCodeImage(string strUrl)
    {

        try
        {
            System.Net.Http.HttpClient client = new System.Net.Http.HttpClient();
            Byte[] bytes = client.GetByteArrayAsync(strUrl).Result;
            // return new MemoryStream(bytes);

            byte[] tt = bytes; //StreamToBytes(stream);//将数据流转为byte[]  

            //在文件名前面加上时间，以防重名  
            string imgName = DateTime.Now.ToString("yyyyMMddhhmmss") + ".jpg";
            //文件存储相对于当前应用目录的虚拟目录  
            string path = "/Uploads/imageminiqrcode/";
            //获取相对于应用的基目录,创建目录  
            string imgPath = System.Web.HttpContext.Current.Server.MapPath(path); //通过此对象获取文件名  

            if (!System.IO.Directory.Exists(imgPath)) //如果文件夹不存在则创建
            {
                System.IO.Directory.CreateDirectory(imgPath);
            }

            System.IO.File.WriteAllBytes(HttpContext.Current.Server.MapPath(path + imgName), tt);//讲byte[]存储为图片  

        }
        catch
        {
            throw new Exception("获取二维码图片失败！");
        }
    }

    ///将数据流转为byte[]  
    public static byte[] StreamToBytes(Stream stream)
    {
        List<byte> bytes = new List<byte>();
        int temp = stream.ReadByte();
        while (temp != -1)
        {
            bytes.Add((byte)temp);
            temp = stream.ReadByte();
        }
        return bytes.ToArray();
    }

protected void Page_Load(object sender, EventArgs e)
    {
　　　　//"https://mp.weixin.qq.com/cgi-bin/showqrcode?ticket=gQEE8jwAAAAAAAAAAS5odHRwOi8vd2VpeGluLnFxLmNvbS9xLzAyMVFYY0pjbl84TVQxMDAwMDAwN2MAAgSytOxYAwQAAAAA"

　　　　SaveQrCodeImage("https://mp.weixin.qq.com/cgi-bin/showqrcode?ticket=gQEE8jwAAAAAAAAAAS5odHRwOi8vd2VpeGluLnFxLmNvbS9xLzAyMVFYY0pjbl84TVQxMDAwMDAwN2MAAgSytOxYAwQAAAAA");
 }