为了使语言的精炼，达到言简意赅的效果, 我们常将状语从句进行"简化"。状语从句的"简化"现象在口语中很普遍, 因此,有必要对其进行全面、透彻的了解。下面，小编应头条友友自由自在等要求为大家整理了相关的语法知识：
首先必须明白最基本的要求是状语从句同时具备下列两个条件: ①主句和从句的主语一致，或从句主语为it； ②从句主要动词是be的某种形式。从句中的主语和be动词常可省略。
注：省略后常常呈现为when,while,as,if,unless,until,once,evenif/though,than等+分词.例如：
When crossing (=When you are crossing) the street, you should be careful.
While studying (While I was studying) at college, I knew a lot of foreign friends.
If heated (If water is heated),water can be changed into vapor.
Unless invited (=Uuless I am invited),I won’t go to the evening party.
Even if/though invited (Even if/though I am invited),I won’t go to his birthday party.
Once seen (=Once the film is seen),the film will never be forgotten.
Our Chinese team has won the match as expected (as it is expected).
When ( the museum is ) completed , the museum will be open to the public next year .
He’ll go to the seaside for his holiday if (it is ) possible.
另外，比较状语从句经常省略。
例如：
I’m taller than he (is tall ).
The higher the temperature (is), the greater the pressure (is ).温度越高，压力就会越大。
以上状语从句的"简化"现象可以看出这些省略形式常存在于以下五种状语从句中:（以上均有例句）
①由if, unless等引导的条件状语从句;
②由although, though, even if / though等引导的让步状语从句;
③由when, while, as, before, after, until / till等引导的时间状语从句;
④由as, as if等引导的方式状语从句;
⑤由as, than等引导的比较状语从句。下面针对这五种情形作一归纳。
(1)当状语从句的主语和主句的主语一致时,从句可以将主语和be动词简化掉。省略后常常以下面几种情形呈现:
a.连词+形容词
Work hard when (you are) young, or you'll regret.少壮不努力,老大徒伤悲。
As (he was) young, he learned how to ride a bike.他小时候就学会了骑自行车。
注：与as引导让步状语从句（as=though 但是as句语气要强一些）位于句首倒装可不是一回事哦，请看：
Strange as it may seem ,it is true.尽管这个事情看上去很奇怪，但却是真的。
Happy as they were, there was something missing.
尽管他们很快乐，但总缺少点什么
Try as he might (= however hard he tried) , he couldn't open the door.
他想尽了办法也没能打开门。
Hard as he works, he can't support his family.
他工作努力，可还是无法养活一家人。
Pretty as she is, no one likes her.
她很美丽，但没人喜欢她。
Although small, the kitchen is well designed.
厨房虽小，但设计巧妙。
Although large in area, the flat did not have many rooms.
这套公寓虽然面积很大，但并没有太多房间。
b.连词+名词
Though (he is) certainly not a lady-killer, he is still very attractive.
他虽然还不至于让女人一见倾心，却很有魅力。（省略结构）
Although (he was) a farmer, now he is a famous director.尽管他曾是个农民,而现在是位著名的导演了。
c.连词+现在分词
Although (he is) doing his best in maths these days, he has still got no good marks.尽管近来他一直在努力学习数学,但他仍然没有取得好成绩。
Though (he is) living alone, he is very happy.
他虽然一个人生活，但很愉快。
Strange though it may sound, I was pleased it was over.（倒装结构）
尽管听起来也许很奇怪，但我很高兴这都结束了。
d.连词+过去分词
There's no snake known that will habitually attack human beings unless threatened
with its life
除非自己的生命受到了威胁，已知的蛇中还没有习惯性地攻击人类的
He won't go there with us unless (he is) invited.除非受到邀请,否则他不会和我们一道去那里。
The concert was a great success than (it was) expected.这场音乐会出乎意料地取得了巨大成功。
e.连词+不定式
He stood up as if (he were) to say something.当时他站起来好像要说什么。He wouldn't solve the problem even if (he were) to take charge.即使他来负责,他也解决不了这个问题。
f. 连词+介词短语
She looked anxious as though (she was) in trouble.她看上去很焦急,好像遇到了麻烦。
He had mastered the English language before (he was) in the USA.他到美国之前就懂英语了。
注意:当从句主语和主句主语不一致时,从句部分要么用老老实实的完全形式,要么嘚瑟就用独立主格结构来表达。例如:
When the meeting was over, all the people went out of the meeting-room.当会议结束时,人们都走出了会议室。（土人表达法）
The meeting being over, all the people went out of the meeting-room.(独立主格结构，比较高逼格表达法)
(2)当状语从句的主语是it,且谓语动词是be时,it和be要完全简化掉。
例如:
If (it is) possible, he will help you out of the difficulty.如果可能的话,他会帮你摆脱困境。
I need to see you, right away if possible.
我要见你，如果可能，马上。
Please make your decision as soon as possible
请尽快作决定。
Some saldiers would ask him about the threequestions whenever possible (=whenever it waspossible).
You’r better not look up new words in thedictionary when you reading unless necessary(=untess it is necessary).
You must attend the meeting unless (it is) inconvenient to you.除非情况对你来说不方便,否则你必须出席这次会议。
(3)状语从句是there be句型时，则there be可省略
例如：
Correct the mistakes in the follwing sentences if any (=if there is any)
要对有错误的句子进行订正。