近几年高考试卷中有关as一词的题目出现过很多次，其中as或是最佳选项，接下来要给大家分享的是定语从句as的用法，欢迎大家的借鉴阅读！
定语从句as的用法
一、用作连词的as
1. 引导时间状语从句，表示“当……的时候”，其用法与when和while类似。例如：As a child (When he was a child), she was sent to six different schools.此用法中as多表示从句与主句动作同时进行，意为“一边……一边……”，一般不与状态动词连用。例如：She sang songs as she did her homework.
as 还可以表示一动作紧接着另一动作发生，说明另一动作的结果，有“随着……”的含义。例如：As time went by, we found he was an honest man./As he grew older, he lost interest in everything except gardening.
例1 It wasn’t until nearly a month later________ I received the manager’s reply.
A. since B. when C. as D. that
解析：本题的as中与when一起作为干扰项，容易使考生往时间状语从句上思考，事实上本题是强调句，正确选项是D。
2. 引导原因状语从句，表示“由于，因为”，相当于because, 但通常置于句首。例如： As he is a qualified doctor, I trust his advice on medical matters.
例2 _____ modeling business is by no means easy to get into, the good model will always be in demand.
A. While B. Since C. As D. If
解析：本题中as干扰性很强，很多考生误以为是原因状语从句，但仔细分析不难发现正确答案应是A(while表示“只要”)。
3. 引导让步状语从句，通常可与although或though通用，但语序不同，although或though用于句首，as用于倒装结构。例如：Young as I am, I already know what career I want to follow. /Although(或Though)I am young, I already know what career I want to follow. as 表示让步用于倒装结构，通常将从句的表语、状语或动词前置。如果表语有冠词a/an, 需去掉。例如：Great scholar as he is, he is lacking in common sense./Much as I like you, I couldn’t live with you. 例3 _____ he has limited technical knowledge, the older worker has a lot of experience.
A. SinceB. Unless C. As D. Although
解析：as 虽然有引导让步状语从句用法，但本题不是倒装结构，故正确答案应是D。
4. 引导方式状语从句，表示“如，像”。例如：When in Rome, do as Romans do./Do to others as you would have others do to you.
例4 We wanted to get home before dark, but it didn’t quite ________ as planned.
A. make outB. turn out C. go onD. come up
解析：本题考查动词词组辨析，题干中的“as planned”给同学们提供了重要信息，答案选B。
5. 固定句型：“主句，as +be/do+主语”表示“也一样”。例如：She’s unusually tall, as are both her parents./He’s a doctor, as was his wife before she had children.
二、用作介词的as
1.表示“如，像”。例如：They got united as one man./She spoke of me as her dearest friend.
2.表示“作为、当作”。例如：As a League member, you should think more of others.
3.与某些动词搭配，表示“把……当作……”，如：look on…as…, regard…as…, treat…as…, consider…as…, think of…as…, see…as…等。其中consider…as…中的as可以省略。as与famous或known搭配，表示“作为……而出名”。
例5 Linda worked for the Minnesota Manufacturing and Mining Company, ________ as 3M.
A. knowingB. known C. being knownD. to be known
解析：如果熟悉be known as这一短语，运用有关非谓语动词的常识，可选出正确答案B。
三、用作关系代词的as
1. 引导限制性定语从句，先行词前通常有as, so, such, same等修饰语。例如：He will marry as pretty a girl as he can find./My hometown is no longer the same as it used to be./As many people as are present will be given a present.在此种用法中，同学们要注意与结果状语从句的区别。比如：A: The teacher asked us such a difficult question that none of us could answer it. B: The teacher asked us such a difficult question as none of us could answer.A句为结果状语从句，而B句则是定语从句。
2. 引导非限制性定语从句，用来指代整个主句(即先行句)，表示“这一事实，那一情况”。从句可以位于句首、句中或句末。例如：We stand when the national anthem is played, as is the custom.
例6 ______ I explained on the telephone, your request will be considered at the next meeting.
A. When B. After C. As D. Since
解析：根据句意，选项C是正确答案。as表现的正是本点所讲用法。
四、用作副词的as
修饰形容词或副词，表示程度，意为“同样地”。例如：He swims fast, but I swim just as fast. 但它通常构成表示比较的.结构“asas”，“not asas”。此结构中第一个as是副词，第二个as是连词。否定结构中的副词as可以由so代替。asas possible /one can也属于此用法。例如：It is generally believed that teaching is as much an art as it is a science.
五、用在习语中的as
由as构成的习语很多，常见的有：as soon as “一就”，引导时间状语从句;as/so long as “只要”引导条件状语从句;as if/though “好像，仿佛”，引导方式状语从句或表语从句;as to/ as for “至于，就而言”;as much/many as“多达”;as/so far as “就的限度”;as a result，as a result of “(由于的)结果”;as a matter of fact“事实上”;as well “也、还”;A as well as B“不但A而且B”;as it is“照现状看，看样子”，等等。这些习语在高考中可能经常遇到，在高考题中有的作为正确选项，有的作为干扰项，有的出现在题干，值得同学们认真掌握。例如：
例9 I would like a job which pays more, but ______ I enjoy the work I’m doing at the moment.
A. in other wordsB. on the other hand C. for one thing D. as a matter of fact 解析：选项D极具干扰意义，但进一步研读会发现本题中的两个分句表达了一件事的两个对立面，故选B。
例10 ——People should stop using their cars and start using public transport. ——______. The roads are too crowded as it is.
A. All right B. Exactly C. Go aheadD. Fine
解析：本题选项中虽没有as内容，但题干中的as it is却是解题的关键信息，正确选项为B。