介词短语在句子中充当表语、状语、定语和补语。常用介词短语有：at once立刻；at last最后；at first起先，首先；with the help of...在……的帮助下；with a smile面带笑容；with one's own eyes亲眼看见；in fact事实上；in a hurry匆忙等。

介词短语可以用作表语

Mr. Smith is still in bed. 史密斯先生还在睡觉。

He was already in his sixties. 他已经六十多岁了。

Dinner was at one o’clock. 一点钟开午饭。

We are out of food. 我们的食物吃完了。

介词短语可以用作状语

The children are playing by the river. 孩子们在河边玩。

They often talk in English after class. 他们经常在课后用英语交谈。

Let’s go out for a walk along the river. 咱们到江边散散步。

介词短语可以用作定语

The woman in the room is his wife. 房间里的那个女人是他的妻子。

China is a country with a long history. 是一个历史悠久的。

注意：介词短语作定语时必须置于被修饰名词之后。

the people on the bus 公共汽车上的人

the girl in front of me 我前面的女孩

a woman in black 一个穿黑衣的妇女

a book on sports 一本关于运动的书

a boy with red hair 红头发的男孩

a bird in the tree 树上的鸟

介词短语可以用作宾语补足语

We found her in tears. 我们发现她在哭泣。

The cold kept him in bed for three days. 这次感冒让他卧床三天。

注意：当含有宾语补足语的句子变成被动语态后，原来的宾语补足语就变成了主语补足语。如：

She was found in tears.（主语补足语）