System.Convert.ToString(int.Parse(str),16);

------解决方案--------------------

C# code

string ShowTxt(byte[] myBytes)
{
  string result;
  foreach(byte b in myBytes)
  {
    string val=Convert.ToString(b, 16);
    result+=(val.length==2?val:"0"+val)+" ";
  }
  return result;
}