过去完成时主要表示过去某一时刻或某一动作之前的动作、状态，有时也表示过去某一时刻之前发生的动作或状态持续到过去另一时间结束。如：
When I turned around, the boy had disappeared. 我一转身男孩就不见了。
He asked if Mary had been sent to hospital. 他问玛丽是否已被送进医院。
注：某些表示“想法”的动词(如intend / think / plan / expect / hope等)的过去完成时表示主语未曾实现的愿望、希望或打算。如：
He had hoped to find a job soon. 他本来希望很快找到工作。
I had intended to come to see you last night, but someone called and I couldn’t get away. 我原打算昨晚来看你，但有人来访，我拖不开身。
若意思明确，以上过去完成时有时可用一般过去时代替。
另外，在hardly / scarcely…when…和no sooner…than 这类固定结构中，主句时态总是要用过去完成时。如：
We had no sooner set out than a thunderstorm broke. 我们刚出发就下起一阵雷暴。
Hardly were the words uttered than he began to regret them. 话刚说出口他就开始后悔了。