string msg= Encoding.UTF8.GetString(Encoding.UTF8.GetBytes(strcode)); 

string strcode="我是小明";
byte[] buffer=Encoding.UTF8.GetBytes(strcode);
string msg= Encoding.UTF8.GetString(buffer,0,buffer.Length);

/// <summary>
 /// 按字節(jié)數(shù)截取字符串的方法(比SubString好用)
 /// </summary>
 /// <param name="source">要截取的字符串（可空）</param>
 /// <param name="NumberOfBytes">要截取的字節(jié)數(shù)</param>
 /// <param name="encoding">System.Text.Encoding</param>
 /// <param name="suffix">結(jié)果字符串的后綴（超出部分顯示為該后綴）</param>
 /// <returns></returns>
 public static string SubStringByBytes(string source, int NumberOfBytes, System.Text.Encoding encoding, string suffix = "...")
 {
  if(string.IsNullOrWhiteSpace(source) || source.Length == 0)
  return source;

  if(encoding.GetBytes(source).Length <= NumberOfBytes)
  return source;

  long tempLen = 0;
  StringBuilder sb = new StringBuilder();
  foreach(var c in source)
  {
  Char[] _charArr = new Char[] { c };
  byte[] _charBytes = encoding.GetBytes(_charArr);
  if((tempLen + _charBytes.Length) > NumberOfBytes)
  {
   if(!string.IsNullOrWhiteSpace(suffix))
   sb.Append(suffix);
   break;
  }
  else
  {
   tempLen += _charBytes.Length;
   sb.Append(encoding.GetString(_charBytes));
  }
  }
  return sb.ToString();
 }
 /// <summary>
 /// 按字節(jié)數(shù)截取字符串的方法(比SubString好用)
 /// </summary>
 /// <param name="source">要截取的字符串（可空）</param>
 /// <param name="NumberOfBytes">要截取的字節(jié)數(shù)</param>
 /// <param name="encoding">UTF-8，Unicode，GB2312...</param>
 /// <param name="suffix">結(jié)果字符串的后綴（超出部分顯示為該后綴）</param>
 /// <returns></returns>
 public static string SubStringByBytes(string source, int NumberOfBytes, string encoding = "UTF-8", string suffix = "...")
 {
  return SubStringByBytes(source, NumberOfBytes, Encoding.GetEncoding(encoding), suffix);
 }