使用ThoughtWorks.QRCode.dll 生成二维码，还需要用到Gma.QrCodeNet.Encoding.Net45.dll 这两个DLL请自行下载，百度一搜一大堆。

    /// <summary>
    /// 获取二维码
    /// </summary>
    /// <param name="strContent">待编码的字符</param>
    /// <param name="ms">输出流</param>
    ///<returns>True if the encoding succeeded, false if the content is empty or too large to fit in a QR code</returns>
    public static void GetQRCode2(string strContent, MemoryStream ms)
    {
        string Content = strContent;//待编码内容
        QRCodeEncoder qrCodeEncoder = new QRCodeEncoder();
        qrCodeEncoder.QRCodeEncodeMode = QRCodeEncoder.ENCODE_MODE.BYTE;//编码方法(注意：BYTE能支持中文，ALPHA_NUMERIC扫描出来的都是数字)
        qrCodeEncoder.QRCodeScale = 4;//大小
        qrCodeEncoder.QRCodeVersion = 0;//版本(注意：设置为0主要是防止编码的字符串太长时发生错误)
        qrCodeEncoder.QRCodeErrorCorrect = QRCodeEncoder.ERROR_CORRECTION.M;
        System.Drawing.Bitmap bp = qrCodeEncoder.Encode(Content, Encoding.GetEncoding("GB2312"));
        bp.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
    }

    /// <summary>
    /// 获取二维码
    /// </summary>
    /// <param name="strContent">待编码的字符</param>
    /// <param name="ms">输出流</param>
    ///<returns>True if the encoding succeeded, false if the content is empty or too large to fit in a QR code</returns>
    public static bool GetQRCode(string strContent, MemoryStream ms)
    {
        ErrorCorrectionLevel Ecl = ErrorCorrectionLevel.M; //误差校正水平 
        string Content = strContent;//待编码内容
        QuietZoneModules QuietZones = QuietZoneModules.Two;  //空白区域 
        int ModuleSize = 12;//大小
        var encoder = new QrEncoder(Ecl);
        QrCode qr;
        if (encoder.TryEncode(Content, out qr))//对内容进行编码，并保存生成的矩阵
        {
            var render = new GraphicsRenderer(new FixedModuleSize(ModuleSize, QuietZones));
            render.WriteToStream(qr.Matrix, ImageFormat.Png, ms);
        }
        else
        {
            return false;
        }
        return true;
    }