过去完成时由“had + 过去分词”构成，表示在过去某一时刻或某一动作之前发生的动作或状态，句中常用by，before，until，when等词引导时间状语。
We had built five new buildings by the end of last year.
(1)肯定结构：主语+ had been done +其他成分
(2)否定结构：主语+ had not been done +其他成分
(3)疑问句结构：had +主语+ been done +其他成分;
疑问词+ had +主语+ been done +其他成分
By the time he got to the school, the first period had been finished.
The classroom hadn't been cleaned before the teacher came.
How many buildings had been destroyed when the hurricane ended?
Had the new plan been discussed before the meeting?
(2)在 told, said, knew, heard, thought等动词之后的宾语从句中，若表示过去某一被动动作时，用过去完成时。
The said the production costs had been reduced.
The boy was reminded that his homework had not been handed in.
The media reported more than 1,000 people had been killed in the earthquake.
As the assignment had been done, he went on to search the Internet.
He did what he had been told to
另：当从句由 after，before，when或 as soon as引导时，主句和从句都可以用一般过去时。
When he arrived, he called her.
They locked the door before they left.