after几种用法：
一、after作介词的用法：
r+名词，作为介宾短语，
如：after 5 o'clock。五点以后。
He ran after the bus.他在那辆公交车后追着跑。
r+动名词，也是作为介宾短语，
如：after having finished my homework。完成我的作业后。
I will go to bed after drinking the milk.
r+代词，作为宾语的主语，
如：He went home after he finished all the work
二、after做副词的用法：
如：three hours after三小时后; He told me after that he had not enjoyed the film.他告诉我后来他一点都不想看电影。
三、after做连词的用法：
如：I saw them after I arrived.我到了之后才看到他们。
用作连词引导时间状语从句时注意：若主句用将来时态(或含有将来意味)，则时间状语从句要用一般现在时态 (表将来意义)表将来意义，而不能直接使用将来时态：他回来后我就走。正：I’ll leave after he comes back.误：I’ll leave after he will come back.
after前后时态
1、遵循“主将从现”原则。
如：He will go to Beijing to work after he graduates from the university.
他大学毕业后将去北京工作。
2、从句表示的`动作发生在主句动作之前，如果强调从句的动作发生在前，从句谓语要用过去完成时，主句用一般过去时。
如：He went out for a walk after he had finished the work.
他完成这项工作后他出去散步。
3、从句表示的动作发生在主句动作之前，如不强调动作的先后，主句和从句均用一般过去时。
如：He went to bed after he finished his homework last night.
昨晚他完成作业后上床睡觉。