一、语态概述
英语的语态是通过动词形式的变化表现出来的。英语中有两种语态：主动语态和被动语态。
主动语态表示主语是动作的执行者。巧记为：主动、主动、主去动。
例如：Many people speak English.
谓语：speak的动作是由主语many people来执行的。
被动语态表示主语是动作的承受者，即行为动作的对象。巧记为：被动、被动、主被动。例如：English is spoken by many people.主语English是动词speak的承受者。
主动态和被动态指的是动词形式，是词法概念；而主动句和被动句则指的是句子结构，从而是句法概念。所谓主动句就是由主动态动词(词组)作谓语动词的句子，而被动句则是由被动态动词(词组)作谓语动词的句子。
例如：He opened the door.他开了门。(主动句)
The door was opened.门被开了。(被动句)
二、被动语态的构成
被动语态由“助动词be＋及物动词的过去分词”构成。人称、数和时态的变化是通过be的变化表现出来的。现以teach为例说明被动语态在各种时态中的构成。
一般现在时：am／is／are＋taught
一般过去时：was／were＋taught
一般将来时：will／shall be＋taught
现在进行时：am／is／are being＋taught
过去进行时：have／has been＋taught
现在完成时：have／has been＋taught
歌诀是：被动语态be字变，过去分词跟后面。
三、被动语态的用法
(1)不知道或没有必要说明动作的执行者是谁。
例如：
Some new computers were stolen last night.
一些新电脑在昨晚被盗了。(不知道电脑是谁偷的)
This book was published in 1981.这本书出版于1981年。
(2)强调动作的承受者，而不强调动作的执行者。
例如：the window was broken by Mike.窗户是迈克打破的。
This book was written by him.这本书是他写的。
Eight hours per day for sleep must be guaranteed.每天8小时睡眠必须得到保证。
歌诀：谁做的动作不知道，说出谁做的没有必要；
动作承受者需强调，被动语态运用到。
四、主动语态变被动语态的方法
(1)把主动语态的宾语变为被动语态的主语。
(2)把谓语变成被动结构(be＋过去分词)
(根据被动语态句子里的主语的人称和数，以及原来主动语态句子中动词的时态来决定be的形式)。
(3)把主动语态中的主语放在介词by之后作宾语，将主格改为宾格。例如：
All the people laughed at him.
He was laughed at by all people.
They make the bikes in the factory.
The bikes are made�by them in the factory.
歌诀是：宾变主，主变宾，by短语后面跟。
谓语动词变被动，be后“过分”来使用。
五、含有情态动词的被动语态
含有情态动词的主动句变成被动句时，由“情态动词＋be＋过去分词”构成，原来带to的情态动词变成被动语态后“to”仍要保留。
歌诀是：情态动词变动，情态加be加“过分”，原来带to要保留。例如：
We can repair this watch in two days.
This watch can be repaired in two days.
You ought to take it away.
It ought to be taken away.
They should do it at once.
It should be done at once.(阜成路中学 司军萍)
不用被动语态的情况
1) 不及物动词或动词短语无被动语态：
appear, die disappear, end (vi. 结束), fail, happen, last, lie, remain, sit, spread, stand
break out, come true, fall asleep, keep silence, lose heart, take place.
After the fire, very little remained of my house.
比较： rise, fall, happen是不及物动词；raise, seat是及物动词。
(错) The price has been risen.
(对) The price has risen.
(错) The accident was happened last week.
(对) The accident happened last week.
(错) The price has raised.
(对) The price has been raised.
(错) Please seat.
(对) Please be seated.
要想正确地使用被动语态，就须注意哪些动词是及物的，哪些是不及物的。特别是一词多义的动词往往有两种用法。解决这一问题唯有在学习过程中多留意积累。
2) 不能用于被动语态的及物动词或动词短语：
fit, have, hold, marry, own, wish, cost, notice, watch agree with, arrive at / in, shake hands with, succeed in, suffer from, happen to, take part in, walk into, belong to
This key just fits the lock.
Your story agrees with what had already been heard.
3) 系动词无被动语态：
appear, be become, fall, feel, get, grow, keep, look, remain, seem, smell, sound, stay, taste, turn
It sounds good.
4) 带同源宾语的及物动词，反身代词，相互代词，不能用于被动语态：
die, death, dream, live, life
She dreamed a bad dream last night.
5) 当宾语是不定式时，很少用于被动语态。
(对) She likes to swim.
(错) To swim is liked by her.
参考资料：
http://www.hongen.com/eng/pub/yufac/1204.htm 参考资料：
http://www.zhongkao.cn/Article_D/2005-08/459456426281451.htm老了不死，慢慢看吧