He has been to Beijing他去过北京,（现在已经回来了,已经不在北京）.
He has been in Beijing.后面必须加一段时间,如 for three years,他已经在北京呆.了.
另外还有一个值得注意
he has gone to Beijing.他去北京了,(可能在路上,可能在北京,反正现在还没回来)