完成式表示的动作或状态发生在谓语动词表示的动作或状态之前。下面举例说明一下。
如：
I am sorry to have kept you waiting. (=I am sorry that I have kept you waiting)
对不起，让你久等了。
注意：
若谓语表示愿望、打算、意图的动词时。
如hope，think，want，plan，expect，mean，
intend等，其后可以跟不定式的完成式表示本来想要或打算做某事，而实际上未能实现。
如：
We meant to have stopped him from doing such a thing.
不定式完成式的用法
1、表示发生在谓语动作之前的动作：
He seems to have caught a cold.
他似乎感冒了。
I hate to have quarreled with her.
我后悔和她吵架了。
I believe it to have been a mistake.
我相信这是一个错误。
You appear to have travelled quite a lot.
你似乎作过多次旅行。
Im sorry to have given you so much trouble.
对不起给了你这么多麻烦。
Its said to have been built in the Ming dynasty.
据说它是明朝修建的。
2、表示在某个给定的时间之前已完成的动作：
I hope to have finished the work by now.
我希望现在以前已完成这项工作。
3、表示过去未曾实现的想法和愿望：
I should like to have come earlier.
我本想早点来的。
We were to have been married last year.
我们本来打算去年结婚的。