示例一

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace UnicodeTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = "this is a 中文字符串! to unicode.";

            string ts = CNStringToUnicode(s);
            string os = Regex.Unescape(ts);

            Console.WriteLine("原字符串："+s);
            Console.WriteLine("转换后的字符串："+ts);
            Console.WriteLine("还原字符串："+os);

            Console.Read();
        }

        //仅把字符串中的中文转成unicode其它字符保持不变
        public static string CNStringToUnicode(string s)
        {
            string uni_str = "";
            for (int l = 0; l < s.Length; l++)
            {
                int c = s[l];
                if (c > 255)
                {
                    uni_str += "\\u" + c.ToString("x").ToUpper();
                }
                else
                {
                    uni_str += (char)c;
                }
            }
            return uni_str;
        }
    }
}

运行测试