1.As可以引导定语从句.有时可译为“正如”.此时,常常是as从句在前,主句在后.
例如：As we can see,he is a Chinese.
2.As 还可引导原因状语从句,“因为,由于”
例如：As he is so lazy,he never cooks by himself.
3.As还可引导时间状语从句,“当,随着”
例如：As the weather is colder and colder,the leaves of the tree is less and less.
4.As还可引导方式状语从句,“按照”
例如：You must do the work as I have told you.
5.As还可引导让步状语从句.“尽管”.但是注意,as引导方式状语从句时从句必须倒装.而且这种倒装和一般的倒装不一样.as从句的倒装一般是把从句的表语或作状语的副词提到as之前,（如果表语是一个带有不定冠词a或an的单数名词,倒装后a或an必须省略).
例如：Though he is a little boy,he knows a lot.如果变成由AS引导,就必须变成：
Little boy as he is,he knows a lot.
Though he works hard,he never succeed.
可变为 Hard as he works,he never succeed.