DECLARE @Table TABLE ( instanceName  sysname NULL)

insert @Table EXEC sys.xp_cmdshell 'sqlcmd -Lc'

--LEFT(@@serverName,CHARINDEX('/',@@serverName+'/')-1) 替代為本機名就行了 , 根據實例命名規則判斷

SELECT * FROM @Table WHERE instanceName LIKE   LEFT( @@serverName , CHARINDEX ( '/' , @@serverName + '/' )- 1)+ '%'

using System;
using Microsoft.Win32;

namespace SMOTest
{
    class Program
    {
      static void Main()
      {
        RegistryKey rk = Registry.LocalMachine.OpenSubKey(@"SOFTWARE/Microsoft/Microsoft SQL Server");
        String[] instances = (String[])rk.GetValue("InstalledInstances");
        if (instances.Length > 0)
        {
           foreach (String element in instances)
           {
              if (element == "MSSQLSERVER")
                 Console.WriteLine(System.Environment.MachineName);
              else
                 Console.WriteLine(System.Environment.MachineName + @"/" + element);
           }
        }
      }
    }
}

public static List GetSQLServerInstances()
{
NameList sqlNameList = null;
Application app = null;

var sqlServers = new List();
try
{
app = new ApplicationClass();
sqlNameList = app.ListAvailableSQLServers();
foreach (string sqlServer in sqlNameList)
sqlServers.Add(sqlServer);
}
catch(Exception ex)
{
//play with the exception.
}
finally
{
if (sqlNameList != null)
sqlNameList = null;
if (app != null)
app = null;
}
return sqlServers;
}