源代码：

namespace ConsoleApplication1
{

    class Program
    {
        static void Main()
        {
            var data = "{\"C_Describe\":\"测试\",\"FY_Subtitle\":\"测试\",\"MAX_ZJ\":20000,\"HType\":\"WFB\",\"communityID\":\"28075\",
　　　　　　　　　　　　　　\"FY_id\":110352,\"areaID\":11,\"IsPublisher\":\"0\",\"attURL\":\"\"}";
            dynamic jsonData = FromJson<dynamic>(data);

            if (ContainChinese(jsonData.FY_Subtitle_CN))
                Console.WriteLine("1");
            if (ContainChinese((dynamic)jsonData.FY_Subtitle))
                Console.WriteLine("2");
           
            Console.ReadKey();
        }

        /// <summary>
        /// 判断是否包含中文
        /// </summary>
        /// <param name="CString"></param>
        /// <returns></returns>
        public static bool ContainChinese(string CString)
        {
            return Regex.IsMatch(CString??"", @"[\u4e00-\u9fbb]");
        }
        /// <summary>
        /// 将json字符串反序列化为dynamic类型
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="jsonText"></param>
        /// <returns></returns>
        public static T FromJson<T>(string jsonText)
        {
            var json = new JsonSerializer
            {
                NullValueHandling = NullValueHandling.Ignore,
               ObjectCreationHandling = ObjectCreationHandling.Replace,
                MissingMemberHandling = MissingMemberHandling.Ignore,
                ReferenceLoopHandling = ReferenceLoopHandling.Ignore
            };

            var sr = new StringReader(jsonText);
            var reader = new JsonTextReader(sr);
            var result = (T)json.Deserialize(reader, typeof(T));
            reader.Close();

            return result;
        }
    }
}

解决方法

在调用通过json反序列化的dynamic对象时，要先强制转换为对应的类型

代码：

if (ContainChinese((jsonData.FY_Subtitle_CN ?? "").ToString()))
    Console.WriteLine("1");
if (ContainChinese((jsonData.FY_Subtitle ?? "").ToString()))
    Console.WriteLine("2");