int a = Convert.ToInt32(txt1.Text.Trim().Replace('[', ']').Split(']')[1]);
  string b = txt1.Text.Trim().Replace('[', ']').Split(']')[2]; 

string str = "[数字]字符串";
Regex reg = new Regex(@"
([^]+)\](.*)");
string a= Convert.ToInt32( reg.Match(str).Groups[1].Value);
string b= Convert.ToInt32( reg.Match(str).Groups[2].Value);

string tempStr = "[数字]字符串"; 
string pattern = @"
([\s§]∗)
([\s\S]*)";
Regex re = new Regex(pattern); 
string str1 = Regex.Replace(tempStr,pattern,"$1"); 
string str2 = Regex.Replace(tempStr, pattern, "$2");

 /// <summary>
 /// 返回一个字符串数组
 /// </summary>
 /// <param name="str"></param>
 /// <returns></returns>
 public string[] ReturnIDAndName(string str)
 {  
  string[] stringArray = new string[2];  
  Regex reg = new Regex(@"
([^]+)\](.*)");
  stringArray[0]= reg.Match(str).Groups[1].Value;
  stringArray[1] = reg.Match(str).Groups[2].Value;  
  return stringArray;
 } 
 
 /// <summary>
 /// 截取字符串编号
 /// </summary>
 public int ReturnId(string str)
 {
  try
  {
   if (string.IsNullOrEmpty(str))
   {
    return 0;
   }
   Regex regex = new Regex("(?<=\\[)\\d+(?=\\])");
   Match m = regex.Match(str);
   int pid;
   if (!m.Success)
   {
    pid = int.Parse("[" + regex.Match(str).Value + "]");
   }
   return int.Parse(regex.Match(str).Value);
  }
  catch
  {
   return 0;
  }
 }