现在完成时表示一个开始于现在之前（即过去）并且仍在持续或刚刚结束的动作。同理类推，过去完成时用来表示在过去某一时刻之前（即过去的过去）就已开始的动作，这一动作：①在该过去时刻仍然在继续或刚刚停止；②在该过去时刻之前的某一时刻已停止；③在该过去时刻之前的一段时间内重复进行。
（1）表示开始于过去某一时刻之前（即过去的过去）的动作或状态在过去这一时刻仍在持续
具体来说，就是一个动作或状态在过去某一时间之前已经开始，一直持续到这一过去时间，并且到这一过去时间还未结束并仍有可能继续持续下去。

（图中虚线箭头表示动作可能继续持续下去）
例句
a. I had stayed in America for two years when he moved here. （moved是过去的动作，stayed发生在moved之前，即过去的过去；在moved之后stayed动作还将会继续。）
b. I had learned 1000 words by the end of last year. （learned在过去时间the end of last year之前已开始，到“去年底”之后还可能持续。）
c. He had collected ten books of stamps by the end of last month.
d. We had studied English for six years when we entered college.
e. It had snowed for a long time when I woke up.
f.— It’s already 10 o’clock. I guess Bob and Amy won’t be coming to the party.
—They called at nine to say that they’d been held up.
或由上下文明确告知动作或状态持续到过去这一时刻为止：

 
请看例句：
g. Former Japanese Prime Minister, who had been in a coma（昏迷）for six weeks, died of a cerebral（大脑的） infarction（梗死） at a Tokyo hospital.
日本前首相在长达六星期的昏迷之后，因脑梗于东京的一家医院逝世。
h. I had waited for two hours in such a severe winter when she eventually turned up, which of course drove me mad.
i. There had been fifty colleges in our city up till 2013.
（2）表示开始于过去某一时刻之前的动作到过去这一时刻之前即已停止
具体来说就是表示一个动作或状态在过去某一时间之前已经开始，并且到这一过去时间之前即告结束，而并没有持续到这一过去时刻。这时过去完成时的动作通常是短暂动作。

 
例句
a. She had made everything ready before I came.
b. Her baby had fallen asleep when she went into the room.
c. Before John got home, Mary had gone to bed.
d. I had just poured myself a cup of tea when the phone rang. When I came back from answering it, the cup was empty. Somebody had drunk the tea or thrown it away.
（3）表示在过去某一时刻之前开始的动作，在过去这一时刻之前的一段时间内重复发生

 
例句
a. I had written her 100 letters when she finally promised to marry me.
b. I had proposed to her five times, but she still refused to marry me.
（4）过去完成时的其他用法
1）intend，mean，hope，want，plan，suppose，expect，think，propose，wish等动词的过去完成时，可表示过去未能实现的计划、设想、意图或希望等。
例句
a. I had planned to go shopping with you but my mother came to see me just when I was about to go.
b. She had hoped that he would come to date her, but he didn’t show up.
c. I had intended to see you, but I was too busy.
d. They had hoped to see you off at the airport, but they got there too late.
2）用在“It was the +序数词/最高级+ that…”句型中。例如：
Last week I attended an international conference and saw Mr. Machine. It was the third time that I had met him
.