1. 过去完成时表示一个动作或状态在过去某一时间或动作之前已经完成或结束，即发生在过去的过去。如：
When I woke up, it had stopped raining.
我醒来时，雨已经停了。（主句的动作发生在过去的过去）
2. 过去完成时是一个相对的时态，表示的是过去的过去，只有和过去某一时间或某一动作相比较时才使用它。如：
He told me that he had written a new book. (had written 发生在 told 之前 )
3. 过去完成时需要与一个表示过去的时间状语连用，它不能离开过去时间而独立存在。此时多与 already ， yet ， still ， just ， before ， never 等时间副词及 by ， before ， until 等引导的短语或从句连用。
如：Before she came to China, Grace had taught English in a middle school for about five years.
Peter had collected more than 300 Chinese stamps by the time he was ten.
4. 过去完成时表示某一动作或状态在过去某时之前已经开始，一直延续到这一过去时间，而且动作尚未结束，仍然有继续下去的可能。
如： By the end of last year, he had worked in the factory for twenty years. （ had worked 已有了 20 年，还有继续进行下去的可能）