一、介词按其构成可分为：
1.简单介词 at,in,on,to,since,until 等.如：
He's worked there since 1998.
2.复合介词 into,onto,out of 等.如：
She is out of school.她毕业了.
3.二重介词 from under,from behind,from out of,until after,except in 等.如：
I'm from out of town.我是从城外来的.
4.短语介词 because of,instead of,in spite of 等.如：
I went back not because of the rain,but because I was tired.
我回去不是因为下雨,而是因为我累了.
二、介词的作用：
1.表示地点：after,along,at,below,by,of,near,over,through,under 等.如：
Near the village the boys are skating on the ice.男孩子们正在村子附近的冰上滑冰.
They lay down under the shade of a tree.他们躺在一棵树的树阴下.
2.表示时间：about,after,across,at,during,for,in,of,till,until 等.如：
After class he will tell us about the accident.课后他将告诉我们有关事故的情况.
A heavy rain has been falling across three days.一场大雨下了整整三天.
The accident happened during the night.事故发生在夜间.
3.表示动作：at,across,around,on,over,under 等.如：
The earth goes around the sun.地球绕太阳运行.
The car is under repair.汽车在修理中.
4.表示比较：as,like,above,over,with 等.如：
She was something like her sister.她有几份像她的妹妹.
Chinese is much more difficult in contrast with English.和英语相比,汉语难得多.
5.表示原因：about,for,from,with 等.如：
Don't worry about my lessons.不要担心我的功课.
Business kept me from coming.我因事不能来.
He was angry with what I did.他对我所做的很气愤.
6.表示条件：to,with,without 等.如：
Without your advice,he would have failed.没有你的忠告他可能已经失败了.
7.表示手段、方式：as,by,in,with 等.如：
He behaved as a drunkard.他的举止如同醉汉一样.
Learn the new words by heart.记住这些生词.
We see with our eyes.我们用眼睛看.
8.表示距离、数量：from,in,within 等.如：
My house is ten miles from the school.我家离学校十英里.
They were thirty in all.他们总共有三十人.
9.表示目的：as,for 等.如：
I only said it as a joke.我只是把它当作笑话讲的.
It's time for class.到上课的时间了.
10.表示让步：for,with 等.如：
For all his effort,he didn't succeed.虽然他做了一番努力,仍不能成功.
With all his money,he is unhappy.尽管他有钱,但他并不快乐.
for 还可以引导插入语,例如：
I,for one,shall vote against the proposal.我也投票反对这个提议.
