现在完成时
1.表示过去发生的但对现在有影响的动作,可以不用时间状语.也可以和一些表示不定过去的时间状语连用,比如already,yet,ever,never,just,once,recently 等.
1).i have been to Peking many times.我多次去过北京（现在对北京有所了解）
2).he has bought a car.(现在他有车可以开了)
2.表示从过去某时间开始一直延续到现在的动作.一般要跟个表示一段时间的状语since,so far,in recently years,for +时间段.
例如
1）.he has lived here since 1949.
2) he has lived here for 40 years.
过去完成时
表示过去某一时刻以前已经完成的动作,常由by,before等.主要是宾语或定语从句中常见.状语从句也会用到
1）by the end of last year,i had worked in this college for ten years.去年年底是过去时间,而在大学工作十年是在去年年底之前,故用过去完成)
2）he had been a teacher for years before he became a writer.(成为作家是过去式,而做老师是在成为作家之前,过去的过去就用过去完成式)
3）he knew that he had made a mistaken (他知道为过去式,而犯错是在知道之前,过去的过去)
不知清楚了没?