介词是表示词语之间语义关系的词类。介词与其后的名词短语一一“对号入座”对词语的搭配关系更是至关重要。但是在有些情况下，有些介词是可以省略的，有些甚至必须省略。

1. 表示时间的短语中有next，last，one，this，every，each，some，any，all等单词时，省略介词：

Can you go to school next Monday?下周一你能上学吗?

We moved here last year. 我们去年搬到这儿。

You can come any day from Monday to Friday.周一至周五你哪一天来都行。

We have worked all day. 我们已经干了一整天活。

2. today, yesterday, tomorrow, the day before yesterday, the day after tomorrow前，无介词：

It is sunny today. 今天阳光灿烂。

We will go to Beijing tomorrow. 我们明天去北京。

3. 在不定冠词a/an的短语中：three meals a day 一日三餐

4. what time前的at常省：

(At)what time would she come here?她几点钟到这儿?

5. 在last, wait, live, stay等延续动词后，for可省：

I waited several hours and then he finally came. 我等了好几个小时后，他才到。

6. Wh-引导的名词性从句作介词宾语时，前面介词可省：

The little boy had no idea (of) what to do next. 这个小男孩不知道接下来要做什么。

7. 含有height, length, size, shape, age, colour, weight等的短语在句子中做表语时：

She is just (of)the right height to be the model we need. 她身高正适合我们所需模特的要求。

Her shoes are (of) the same size as mine 她的鞋子和我的大小一样。

8. 在in the same way, in this way, in another way等短语中，in常省:

Please try to do it again (in) the same way. 请用同样的方法再做一次。

9. 在口语中，星期前的on常省：

Why don’t you come and play (on) Sunday evening?星期日晚上到我家来玩不好吗?

10. 以下句型中，介词常省：

(1)have (no) difficulty/trouble(in)doing sth做某事有(没)困难/麻烦：

(2)be busy (in) doing忙于做某事

(3)keep sb busy (in) doing sth使某人忙于做某事

(4)spend/ waste time (in) doing sth花时间/浪费时间做某事

(5)There/ It is no use/good (in) doing sth做某事没有用

(6)keep/ prevent/stop sb (from) doing sth 阻止(防止)某人做某事

(7)have a good time (in) doing sth因做某事而开心

(8)lose no time (in) doing sth抓住机会做某事

(9)There is no point (in) doing sth做某事毫无意义

(10)take turns (at) doing sth轮流做某事

(11)end up (by) doing sth以干某事而告终

(12)be engaged (in) doing sth专心做某事

哪些情况下必须要用介词，哪些介词在哪些情况下可以省略，这些都需要我们认真区分，牢牢记住，以免画蛇添足，在使用中犯错。