状语从句在主从复合句中修饰主句中的动词、形容词或副词等，按意义可以分为时间、地点、原因、目的、结果、条件、方式、比较、让步等状语从句。
一.时间状语从句。
通常由从属连词when, whenever, as, while, before, after, as soon as, till, until, since, once (一旦), hardly……when…, no sooner…….than…; 等引导。例如：
The cyclist started just as the lights changed to green.
Whenever we met with difficulties , they cam to help us.
He didn’t leave his office until he had finished the day’s work.
应注意的问题
1.在时间状语从句中，通常要用动词的一般现在时态表示一般将来时态，用一般过去时态表示过去将来时态。但when 引导一般疑问句或名词性从句时不受上述语法规则的限制，因此，应该加以区分。例如：
When China will enter WTO depends on the bilateral (双边的)joint efforts.
Once you understand the rules of the game, you’ll enjoy it.
2.when , while, as 的不同用法。一般说来，当主、从句的动作是同时发生的事，三者可以换用。when 既可以引导一个持续动作，也可以引导一个短暂动作，可用于主句和从句动作同时发生或从句动作先于主句动作;while 引导的动作必须是持续性的，强调主句和从句的动作同时发生，往往侧重主句和从句动作的对比;as 用于引导“在某行为的继续中发生某事”的“继续之行为”，所以多与过去进行时连用，翻译成“一边……一边……”或者表示动作的变化，翻译成“随着……”。
例如：
I hope you’ll think of my words as/when/while you drive on the busy roads.
When he realized it, the chance had been lost.
When he came home, I was cooking dinner.
I was fat when I was a child.
He took a bath while I was preparing dinner.
As I was walking down the street, an American asked me for the directions to the nearest station.
He sang songs as he was taking a bath.
As he gets older he gets more optimistic.
另外还必须注意 when和while 的特殊用法。when 可以表示“就在这时，突然”之意;而while 则可以表示对比的含义，常可译作“而”。例如：
She thought I was talking about her daughter, ____, in fact, I was talking about my daughter.(NMET95)
A. whom B. where C. which D. while
答案：D. 本句的意思是“她认为我在谈论她女儿，然而，实际上，我在谈论我女儿。”
再如：
I was about to go to bed when the phone rang a second time.
我正准备去睡觉，就在这时电话铃又响了。
3.since 和before 的用法区别。两者都可用于 “It + be + since/ before-从句”的句型，区别在于 since 表示“自从…… 以来”，所在主、从句的谓语动词的时态关系是：It is/has been some time since sb did something. 而before 的含义则是“(过了多久)才……”,主、从句的时态关系是：It was/ had been some time before sb did sth。 表示过去和将来时，两者相应的句型分别是：It was some time since sb had done something. 和It will be some time before sb does something. 例如：
It was / had been years before I came back from abroad.
It will be five years before we meet again.
4.一些表示时间的名词词组如： the first time, the second time, last time， the moment, the minute，the year, every time, each time , next time, 或副词immediately, instantly, directly等也可以引导时间状语从句。例如：
I’ll tell you about it the moment you come.
I recognized her the minute I saw her.
I’m going to see him next time he comes to Shanghai.
He left Europe the year World War II broke out.
I got in touch with him immediately I received his letter.
My sister came directly( = as soon as ) she got my message.
5.till 和until
till 和until 意义相同，多数情况下可以换用，但用以强调，句首多用until; 在强调结构或与not 连用时多用until. 例如：
Nothing can be done till/until the boss returns.
We waited till/until they came back.
Until we know the facts, we can’t do anything about it.
Not until midnight did the noise of the street stop.
6.hardly……when和no sooner……than相当于as soon as 之意，也可引导时间状语从句。从句谓语动词用一般过去时，主句谓语动词用过去完成时。hardly 及no sooner 置于句首时，语气较强，主句的谓语要部分倒装。例如：
We had hardly begun when we were told to stop.
= Hardly had we begun when we were told to stop.
The spy had no sooner returned home than he was told to go to another country.
= No sooner had the spy returned home than he was told to go to another country.
二.地点状语从句。
地点状语从句由 where和wherever 引导， 在主句前、后都可。where 表示特指，wherever 则表示泛指。但不少学生易将其和定语从句混淆，再者有的同学对地点状语从句不太注意，所以往往做错。例如：
You should make it a rule to leave things ___ you can find them again. (NMET99)
A.when B.where C.then D.there
答案：B. 注意它引导的不是定语从句。
After living in Paris for fifty years he returned to the small town ____ he grew up as a child.(NMET 96)
A.which B. where C. that D. when
答案：B. 这是一个由where 引导的定语从句，修饰先行词the small town.。再如：
Where there is a will, there’s a way.
