string st="GT123_1";

string[] sArray=st.split("_");

//即可得到sArray[0]="GT123",sArray[1]="1";

string str = "GTAZB_JiangjBen_123";
string[] sArray = str.Split(new char[2] { 'j', '_' });
foreach(string e in sArray)
{
  Console.WriteLine(e);
}

//得到sArray[0]="GTAZB",sArray[1]="Jiang",sArray[2]="Ben",sArray[3]="123";

string str = "GTAZB_JiangjBen_123";
string[] sArray = str.Split( new string[]{"Ji","jB"}, StringSplitOptions.RemoveEmptyEntries);
foreach(string e in sArray)
{
  Console.WriteLine(e);
}

//得到sArray[0]="GTAZB_",sArray[1]="ang",sArray[2]="en_123";

string str = "GTAZB_JiangjBen_123";
int start=3,length=8; 
Console.WriteLine(str.Substring(start-1, length));

//输出得到AZB_Jian。

string str = "GTAZB_JiangjBen_123";
string tSt;
int i=5;
tSt = str.Substring(str.Length - i); 
Console.WriteLine(tSt);

//输出n_123

string str = "GTAZB_JiangjBen_123";
string tSt;
tSt = str.Replace("123","321");
Console.WriteLine(tSt);

//输出GTAZB_JiangjBen_321

string str = "GTAZB_JiangjBen_123";
string tSt;
tSt = str.Replace("Jiangj","");
Console.WriteLine(tSt);

//输出GTAZB_Ben_123

 string str = "GTAZB_JiangjBen_123";

int i=5,length=8;
str=str.remove(i,length);
console.writeline(str);

//输出GTAZBen_123