一、表示比较，意为“象……一样，正如，如同”She’s very tall, as is her mother. 她个子很高，和她母亲一样。
二、表示方式、程度、情况。意即“照……方式、如同、象”They did as I had asked. 他们是按照我的要求做的。
三、表示时间，意为“当……时候”，“一边……一边”“随着……”As he grow older he gained in confidence. 随着年龄的增长他的信心增强了。
四、表示原因，意为“因为，由于”As you were out, I left a message. 你不在，所以我留下了一张字条。
五、表示让步，意为“尽管;虽然;即使”(表语一般放在本从句之首;如有可数名词单数，前面也不要冠词)Child as he is ,he can tell black from white. 尽管他是个孩子，但他能够分辨黑白。Happy as they were, there was something missing. 尽管他们很快乐，但总缺少点什么。
六、引导定语从句1)as引导非限制性定语从句，常指主句所表达的整个事情，可置句首、句中、句末，常见 as we all know,as I see it 照我看来，as it appears to me 依我看来。As we all know, oceans cover more than 70 percent of the earth.正如我们所知道的，海洋占地球面积70%以上。
2)as引导限制性定语从句From every corner of the island little people came to see the "Man Mountain~as they called Gulliver. 小人们从海岛的各个角落来看他们叫做‘人山’的格利佛。
3)as与 such, so, the same 连用，此时先行词是一个具体的名词，as在从句中可作主语、宾语或表语。The book is written in such easy English as beginners can understand. 这本书是用初学者也能读懂的浅易英文写的。She studies in the same department as I do. 他和我在同一个系统学习。Here is so difficult a problem as none of us can solve.这是一个我们都不能解决的难题
