had + 过去分词 例如：I had studied for three hours before I went to bed.（我在睡觉之前学习了三个小时。）She had already eaten breakfast by the time I arrived.（我到达时，她已经吃过早饭了。）
表示过去某个时间点之前已经完成的动作或事件，常常和过去时态连用，用来强调先后顺序。这个时间点可以用介词 before 加上一个具体的时间表示，也可以用其他类似的表达方式。 例如：I had finished my homework before I went to play basketball.（我去打篮球之前，已经完成了我的家庭作业。）Carol had traveled to many countries before she settled down in Japan.（卡罗尔在定居日本之前已经去过很多国家了。）
对话中可以用来表达过去完成的动作或事件，表示“我已经做了…”。例如：'I had already bought the tickets before you asked me to.'（“在你向我询问之前，我已经买了票了。”）
它也可以用于表示虚拟语气，表示过去某个时间点之前本来可以完成，但是最后没有完成，常常和 if 条件句连用。例如：If I had known you were coming, I would have prepared dinner.（如果我知道你要来，我会准备晚餐的。）If I had studied harder, I would have passed the test.（如果我学得更努力，就能通过这次考试了。）END
过去完成时态通常用于表示先后顺序，强调过去某一时间点之前已经完成的动作或事件，也可以用于表示虚拟语气的情况。