which在定语从句中作主语时不能省略，作宾语时可以省略，引导非限制性定语从句时不能省略。
which的用法：
1、先行词是物，在定语从句中作主主语或宾语；
2、which的前面可以有介词；
3、which的先行词可以是前面数个的的句子,意为”这使…….;这一点……”。
A computeris a machine which can do many things for us.
电脑是一种可以为我们做许多事情的机器。( which作主语)
The chair on which she sat is made of wood
她坐的椅子是用木头做的。( which作介词的宾语)
Mo yan was awarded the nobelprize in literature , which made us happy
莫言被授子诺贝尔文学奖，这使我们非常高兴。( which引导非限制性定语从句)
扩展资料
as与which在限制性定语从句中的区别：
1、as 的用法
其通常和such\ the same连用，代指物在从句中做主语或宾语
This is the same pen as I bought yesterday。
这种笔和我昨天买的笔一样（同样的但不是同一个）。引导定语从句的关系词在从句中做宾语，因先行词被the same所修饰所以用as引导
注意：上句与下句的区别 This is the same pen that I used yesterday.这就是昨天我使用的那一支钢笔（指的是同一个）。
2、which的用法
关系代词，在从句中做主语或宾语，做宾语时通常可以省略（直接做介词的宾语时除外，不能省。）
The radio which he bought yesterday doesn't work now.
他昨天买的收音机现在坏了。
引导定语从句的关系代词在从句中做宾语，代指物，故用which.
Here is the man (who/that/whom)you're been looking for.
以下情况不能省略：
（1）在介词+whom与介词+which中，whom,which不能省略。
Do you know any shops nearby in which I can buy flowers?
That is the headmaster with whom my father was talking just now.
注：当介词放在动词后时，which,whom就可以省略。
Who is the man (whom) you talked with just now?
（2）在非限制性定语从句中，作宾语的关系代词也不能省略。
Mr Green,whom you know,is the tallest in our school.
The elephant is like a spear,as anybody can see.
（3）在the same ...as,such...as,as...as,the same...that中，as,that即使作宾语，也不能省略I have bought the same bicycle as you have (bought). (指同类用as)
This is the same book that I read the day before yesterday. (that指同一个)
（4）当由and,but,or等连词连接两个或两个以上的定语从句修饰一个先行词时，第一个关系代词可省，但第二，第三个不可省略。
This is the book (which) I read yesterday and which I find very interesting.
2.当that在从句中作补语时可以省略。
He is not the man (that) he used to be.
She is all (that) a teacher should be.
3.在there be 结构中出现定语从句，或在定语从句中出现there be 时，用作主语的关系代词也可省略。
There is a man downstairs (who) wants to see you.
This is the best dictionary (that) there is in the library.
4.状语的省略
（1）当先行词是reason，而且定语从句中作原因状语时，关系代词可用why,that,也可以省略。
The reason (why/that) he failed was his laziness.
That is the reason (why) I did it.
（2）当先行词是way,且在定语从句中作方式状语时，关系代词可用in which,that,也可以省略。
The way (in which/that) these comrades look at problems is wrong.
That was the way (in which/that) she worked the problem out.
注意：当关系代词在定语从句中作主语时，不省略。
例如：I don't know the way that/ which leads to the top of the mountains.
(3)当先行词是time时，关系代词可用when,that 或省略。
The second time (that) I saw him was in 1980.
I don't know the exact time (when/that) the sports meet will take place.
注意：关系代词作宾语有时也不能省略。本回答被网友采纳