1、

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

di.FullName 就是你想要的

..\有几个就是往回退几层

   2、

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

3、

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