介詞是表示詞語之間語義關系的詞類。介詞與其后的名詞短語一一“對號入座”對詞語的搭配關系更是至關重要。但是在有些情況下，有些介詞是可以省略的，有些甚至必須省略。

1. 表示時間的短語中有next，last，one，this，every，each，some，any，all等單詞時，省略介詞：

Can you go to school next Monday?下周一你能上學嗎?

We moved here last year. 我們去年搬到這兒。

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

We have worked all day. 我們已經干了一整天活。

2. today, yesterday, tomorrow, the day before yesterday, the day after tomorrow前，無介詞：

It is sunny today. 今天陽光燦爛。

We will go to Beijing tomorrow. 我們明天去北京。

3. 在不定冠詞a/an的短語中：three meals a day 一日三餐

4. what time前的at常省：

(At)what time would she come here?她幾點鐘到這兒?

5. 在last, wait, live, stay等延續動詞后，for可省：

I waited several hours and then he finally came. 我等了好幾個小時后，他才到。

6. Wh-引導的名詞性從句作介詞賓語時，前面介詞可省：

The little boy had no idea (of) what to do next. 這個小男孩不知道接下來要做什么。

7. 含有height, length, size, shape, age, colour, weight等的短語在句子中做表語時：

She is just (of)the right height to be the model we need. 她身高正適合我們所需模特的要求。

Her shoes are (of) the same size as mine 她的鞋子和我的大小一樣。

8. 在in the same way, in this way, in another way等短語中，in常省:

Please try to do it again (in) the same way. 請用同樣的方法再做一次。

9. 在口語中，星期前的on常省：

Why don’t you come and play (on) Sunday evening?星期日晚上到我家來玩不好嗎?

10. 以下句型中，介詞常省：

(1)have (no) difficulty/trouble(in)doing sth做某事有(沒)困難/麻煩：

(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花時間/浪費時間做某事

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

(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因做某事而開心

(8)lose no time (in) doing sth抓住機會做某事

(9)There is no point (in) doing sth做某事毫無意義

(10)take turns (at) doing sth輪流做某事

(11)end up (by) doing sth以干某事而告終

(12)be engaged (in) doing sth專心做某事

哪些情況下必須要用介詞，哪些介詞在哪些情況下可以省略，這些都需要我們認真區分，牢牢記住，以免畫蛇添足，在使用中犯錯。