after后面直接跟动词时，要用动词的ing形式，构成 after doing形式的介词短语，after现在分词的动作必须和谓语动作具有时间上的同时性，否则错误。在这里after是做介词用，而介词后面只能跟名词或者是动名词 。
after还可以做连词，后面可以接句子。当after当连词用时，从句是不允许省略主语和be的。因此，后接V-ing形式一定是介词加动名词。介词短语作状语。介词+动名词作状语，主语必须是动名词的逻辑主语。否则就是错误。
例如：
After finishing his homework,he went home. after 做介词，加动名词
After he finished his homework,he went home. after做连词，加句子。
扩展资料:
（1）After hearing the hero speech, the students seem to be greatly inspired.
听完英雄的演讲后，同学们受到很大的鼓舞。
（2）He nestled up against his mother after waking up.
睡醒之后他依然依偎在妈妈身边。
（3）After answering my questions, he slept on.
回答完我的问题后，他又接着睡觉了。
（4）We were heated up after running for about one hour.
跑了近一个小时，我们浑身都发热了。
（5）After finishing breakfast he perused the newspapers.
早饭后，他读了各种报纸。
1、after后面直接加一个动词时，它是作为一个介词，动词用ing形式。
2、after是引导一个从句，从句是一个独立完整的句子，可以用各种时态和语态。
3、after做介词时，后面只能加名词/代词/动名词短语(doing sth)，形成介宾短语，做句子的状语(时间状语/地点状语)。
4、after做连词时，引导一个时间状语从句，意思是“在...之后”。
拓展资料
after
1. No matter where you go in life or how old you get, there's always something new to learn about. After all, life is full of surprises.
不管你生活在哪里，你有多少岁，总有新东西要学习，毕竟，生活总是充满惊喜。
2. He was fired from his job after roughing up a colleague.
他因为对一位同事动粗而被开除了。
3. The mystery hero imme-diately alerted police after spotting a bomb.
那个无名英雄发现炸弹后马上报了警。
4. After a three-weekend courtship, Pamela accepted Randolph's proposal of marriage.
经过3个周末的追求之后，帕梅拉接受了伦道夫的求婚。
5. The ballot was re-run on Mr Todd's insistence after accusations of malpractice.
因被控舞弊，在托德先生的坚持下重新进行了投票。
6. He does deserve some good luck after so much wretchedness.
经过这么多苦难之后，他应该行点好运了。
7. After sixteen years of marriage they have grown bored with each other.
结婚16年后，他们已经渐渐彼此厌倦了。
8. After years of neglect and decline the city was cleaning itself up.
多年的玩忽职守和经济萧条过后，这个城市在进行自我整顿。
9. After his elevation to the papacy, he reigned for two years.
他升任教皇后在位两年。
10. She dropped out after 20 kilometres with stomach trouble.
20公里后她因胃痛而退出了比赛。
2.after是引导一个从句，从句是一个独立完整的句子，从句的时态应该比主句早一个时态,比如：
如果是过去发生的事情 after后接过去完成时
如:I played computer games after I had finished my homework.
如果是将来发生的事情
如:I will play computer games after I finish my homework.
当然也不一定那么严格的 也可以接一般过去时
但是after是引导一个从句，从句是一个独立完整的句子，可以用各种时态和语态。本回答被网友采纳
而是说在介词后动词变ing形式
即afer doing sth...在做了...之后本回答被网友采纳