一）as作副詞，表示程度，意爲“同樣地”。在“as．．．as．．．”，“not as．．．as．．．”結構中的第一個as是副詞，作“和／與．．．(不)一樣”解。eg：
Jack is as tall as his father．傑克和他的父親一樣高。
He doesn't speak English as／so fluently as you．他的英語說得不如你流利。
二）as作介詞。
1．作“如，像”解。eg：
They got united as one man．他們團結得像一個人一樣。
2．作“充當，作爲”解。eg：
As a writer，he was famous．作爲作家，他是很有名的。
三）as作連詞，常用來連接主句和狀語從句。
1．引導時間狀語從句，作“當．．．的時候”解，有“隨着．．．”之意，與while意義相近，強調兩個動作同時發生；或某事一發生，另一事立即發生。eg：
He shouted aloud as her ran along．他一邊往前跑，一邊高聲地呼喊。
I was startled as he opened the door．他一開門，我嚇了一跳。
as作連詞，相當於when。eg；
As a little boy (When he was a little boy)he began to learn to play piano．他小時候就開始學彈鋼琴。
2．引導原因狀語從句，作“因爲，由於”解，與because的用法相近。eg；
I must stop writing now，as I have rather a lot of work to do．我必須停筆了，因爲我還有許多工作要做。
3．引導方式狀語從句或比較狀語從句，作“正如，(如)像”解。例eg：
As in your country，we grow wheat in the north and rice in the south．正如(像)你們國家一樣，我們在北方種小麥，在南方種大米。(方式狀語從句)
When at Rome，do as Romans do．入鄉隨俗。(方式狀語從句)
4．引導讓步狀語從句，作“雖然，儘管”解。這時從句常用倒裝語序，即把從句中的表語、狀語或動詞原形放在as之前。eg；
Strange as it may seem，it is true．儘管這事看上去很奇怪，但卻是真的。
Try as he might，Tom could not get out of the difficulties．不管怎樣努力，湯姆還是擺脫不了困境。
四）as作關係代詞。
1．引導限制性定語從句，用在“such．．．as”,“the same．．．as”，“as．．．as”等結構中，常譯作“像．．．一樣的人(或物)”，“凡是．．．的人(或物)”。例eg：
He wished to be such a man as Lei Feng was．他曾希望做一個像雷鋒那樣的人。
My hometown is no longer the same as it was．我的家鄉再也不像過去一樣了。
2．引導非限制性定語從句，用來指代它前面的整個句子(即先行句)，意思是“這一點”。這個分句可以位於句首、句中或句末。eg：
As is well known，oceans cover more than 70％ of the earth．我們知道，海洋佔地球面積的百分之七十以上。
五）含as的固定詞組的用法
1．as soon as作“一…就”解，引導時間狀語從句。eg：
As soon as I get to Beijing，I'll write to you．我一到北京，就給你寫信。
2．as／so long as作“只要”解，eg；
As／So long as you study hard，you'll make progress．只要你努力，你就會取得進步。
3．as if／though常用來引導方式狀語從句，作“好像，彷彿”解。如果從句中講的是非真實情況，則用虛擬語氣。eg：
She loves the child as if／though he were her own．她愛這個孩子如同愛自己的孩子。
As if／though也可用來引導表語從句，常用在“It appears／looks／seems．．．+as if／though”句型結構中。eg；
It appears as if／though it is going to clear up．看起來天要晴了。
It seems as if／though he knew nothing about it.他好像對此事一無所知。
4．as to作“關於，至於”解。eg；
There is no doubt as to his honesty．他的誠實是無可置疑的。
5．as much／many as作“多達．．．”，“達到．．．之多”解。eg：
He can earn as much as 5000 dollars a month．他每月能掙5000美元。
6．so／as far as I know作“就我所知”解，在句中作插入語。eg：
As／So far as I know，he will come here next Monday．據我所知，他將於下星期一到這裏來。
7．as a result，as a result of表示“由於．．．的結果”。eg：
She died as a direct result of the accident．她的死是那次事故的直接結果。
8，as well爲“也，還”之意。eg：
Come early，and bring your brother as well．早點來，把你的弟弟也帶來。
9．so as to，so．．．as to若跟動詞原形，表示目的或結果。eg：
He studied hard so as to pass the exam．他努力學習以便通過考試。(
Jack is as tall as his father．傑克和他的父親一樣高。
He doesn't speak English as／so fluently as you．他的英語說得不如你流利。
二）as作介詞。
1．作“如，像”解。eg：
They got united as one man．他們團結得像一個人一樣。
2．作“充當，作爲”解。eg：
As a writer，he was famous．作爲作家，他是很有名的。
三）as作連詞，常用來連接主句和狀語從句。
1．引導時間狀語從句，作“當．．．的時候”解，有“隨着．．．”之意，與while意義相近，強調兩個動作同時發生；或某事一發生，另一事立即發生。eg：
He shouted aloud as her ran along．他一邊往前跑，一邊高聲地呼喊。
I was startled as he opened the door．他一開門，我嚇了一跳。
as作連詞，相當於when。eg；
As a little boy (When he was a little boy)he began to learn to play piano．他小時候就開始學彈鋼琴。
2．引導原因狀語從句，作“因爲，由於”解，與because的用法相近。eg；
I must stop writing now，as I have rather a lot of work to do．我必須停筆了，因爲我還有許多工作要做。
3．引導方式狀語從句或比較狀語從句，作“正如，(如)像”解。例eg：
As in your country，we grow wheat in the north and rice in the south．正如(像)你們國家一樣，我們在北方種小麥，在南方種大米。(方式狀語從句)
When at Rome，do as Romans do．入鄉隨俗。(方式狀語從句)
4．引導讓步狀語從句，作“雖然，儘管”解。這時從句常用倒裝語序，即把從句中的表語、狀語或動詞原形放在as之前。eg；
Strange as it may seem，it is true．儘管這事看上去很奇怪，但卻是真的。
Try as he might，Tom could not get out of the difficulties．不管怎樣努力，湯姆還是擺脫不了困境。
四）as作關係代詞。
1．引導限制性定語從句，用在“such．．．as”,“the same．．．as”，“as．．．as”等結構中，常譯作“像．．．一樣的人(或物)”，“凡是．．．的人(或物)”。例eg：
He wished to be such a man as Lei Feng was．他曾希望做一個像雷鋒那樣的人。
My hometown is no longer the same as it was．我的家鄉再也不像過去一樣了。
2．引導非限制性定語從句，用來指代它前面的整個句子(即先行句)，意思是“這一點”。這個分句可以位於句首、句中或句末。eg：
As is well known，oceans cover more than 70％ of the earth．我們知道，海洋佔地球面積的百分之七十以上。
五）含as的固定詞組的用法
1．as soon as作“一…就”解，引導時間狀語從句。eg：
As soon as I get to Beijing，I'll write to you．我一到北京，就給你寫信。
2．as／so long as作“只要”解，eg；
As／So long as you study hard，you'll make progress．只要你努力，你就會取得進步。
3．as if／though常用來引導方式狀語從句，作“好像，彷彿”解。如果從句中講的是非真實情況，則用虛擬語氣。eg：
She loves the child as if／though he were her own．她愛這個孩子如同愛自己的孩子。
As if／though也可用來引導表語從句，常用在“It appears／looks／seems．．．+as if／though”句型結構中。eg；
It appears as if／though it is going to clear up．看起來天要晴了。
It seems as if／though he knew nothing about it.他好像對此事一無所知。
4．as to作“關於，至於”解。eg；
There is no doubt as to his honesty．他的誠實是無可置疑的。
5．as much／many as作“多達．．．”，“達到．．．之多”解。eg：
He can earn as much as 5000 dollars a month．他每月能掙5000美元。
6．so／as far as I know作“就我所知”解，在句中作插入語。eg：
As／So far as I know，he will come here next Monday．據我所知，他將於下星期一到這裏來。
7．as a result，as a result of表示“由於．．．的結果”。eg：
She died as a direct result of the accident．她的死是那次事故的直接結果。
8，as well爲“也，還”之意。eg：
Come early，and bring your brother as well．早點來，把你的弟弟也帶來。
9．so as to，so．．．as to若跟動詞原形，表示目的或結果。eg：
He studied hard so as to pass the exam．他努力學習以便通過考試。(