第一种方法：

DirectoryInfo di = new DirectoryInfo(string.Format(@"{0}..\..\", Application.StartupPath));
 di.FullName

第二种方法：

DirectoryInfo info = new DirectoryInfo(Application.StartupPath);
String path = info.Parent.Parent.FullName;

第三种方法：

string WantedPath = Application.StartupPath.Substring(0,Application.StartupPath.LastIndexOf(@"\"));