1、如果先行词是all, much, anything, something, nothing, everything, little, none等不定代词,关系代词一般只用that,不用which。如：

All that can be done has been done.
能做的都已经做了 。
He will tell you everything that he heard about it.
他将告诉你他所听到的关于这件事的一切。

2、当先行词被all, every, no, some, any, little, much所修饰时，只能用that，如：

There is little work that is fit for you.
没什么工作运合你做。
I have eaten all the food that is left.
我把剩下的所有食物都吃了 。

3、先行词是序数词或最高级形容词时，或者先行词被序数词（包括last，next)、最高级形容词及the only, the very等修饰时。如：

This is the first film that I have seen since I came here.
这是我到这里后所看的第一场电影。
This is the best that has been used against pollution.
这是用来防止污染的最好办法。
This is the very book that I am looking for.
这正是我一直在寻找的那本书。

4、先行词包括人和物时，关系代词应该用that。如：

They often talk about the people and the things that they are interested in.
他们常常谈论那些他们感兴趣的人和事。
Luxun and his works that we are familiar with are considered great.
人们认为我们所熟识的鲁迅及其作品都很伟大。

5、当主句是以who或which升头的疑问句时，为了避免重复，多用that导。如：

Which is the house that caught fire last night?
昨晚失火的是哪座房子？
Who is the lady that is playing the piano?
在弹钢琴的那位小姐是谁？

6、当先行词在定语从句中作表语时，只能用that。如：
This is a book that I have been looking for since last week.
这就是那本自上周以来我一直在寻找的书。

一、that与which的区别（只用that的情况）

当先行词指物时才需要讨论这个问题

1. 当先行词为不定代词，如anything, everything, nothing, none, one, all, little, few, much 等，或先行词被all, little, few, much, any, only, the every, every, no等修饰时，要用that指代先行词

• All that is needed is oil.

• Finally, the thief handed everyting that he had stolen to the police.

• This is the only problem that remains to be settled.

2. 先行词是序数词/最高级形容词时，或先行词被序数词，最高级形容词修饰时，要用that

• This is the first/best film that I have seen since I came here.

3. 先行词同时包括人和物时，要用that

• They often talk about the people and the things that they like most.

4. 避免重复

① 主句的主语是疑问词who或which

• Which is the bike that you have lost?

• Who is the boy that won the gold medal?

② 两个定语从句，其中一个用which另一个用that

• They secretly built up a small factory, which produced things that could cause much pollution.

5. 先行词在主句中作表语,关系词在从句中也作表语

• Shanghai is no longer the city that it used to be.

6. 主句是there be 句型且关系词在从句中作主语

• There is a seat that is still available.

即：限定性定语从句中，万一脑抽无法判断的时候，选that居多

二、不能用that的情况

1. 在非限定性定语从句中不能用that，而用who, whom,which等指代先行词

• I saw Mary just now, who seemed very excited.

2. 介词后不能用that

例：This is the person to whom your father spoke just now.

3. 当先行词是any, few, one(s), anyone, everyone, those, people等且指人时，只能用who, 不用that

• Those who are present will have the chance to see the film star.

4. 先行词本身是that（避免重复）

5. there be结构中先行词指人

• There is a man who calls himself Mr. S joining our team.

以下是定语从句中用who不用that的情况:

1) 当先行词为人称代词 he, she, they 或one(s), anyone, nobody 等时
He who plays a trick must be prepared to take a joke. 玩花招的人必定会受到戏弄。
The ones who refuse to reform should be punished as required by law. 拒绝改革的人应依法受到惩罚。
It was she who first introduced me to the pleasures of wine-tasting. 是她第一个让我领略到品酒的乐趣。
There is nobody who has no shortcomings. 没有缺点的人是没有的。

2) 当先行为指示代词 those，或先行词是those所修饰的人时
This website is dedicated to those who died in the war. 这个网站是献给那些在战争中死去的人。
She is one of those women who always make the worst of their troubles. 她是那些老是把困难往最坏处想的女人之一。

3) 当先行词是序数词或被序数词修饰时
He is the third man who witnessed the murder. 他是这起谋杀案的第三个见证者。
They were the first who were there. 他们是去那里的第一批人。

4) 当先行词是 people 或是表示人的集体名词时
An interactive product should show interest in the people who use it. 一款互动的产品应该展现出对用户的兴趣。
The crew who were all asleep forgot to hoist a lantern. 已入睡的船员全部忘了挂起提灯。

5) 当先行词与定语从句被其他句子成分隔开时。（更多这样的例子可见隔离定语从句一文)
He is the only doctor in this hospital who I trust. 他是这家医院里我唯一信得过的医生。

6）当关系代词在从句中作主语且与谓语动词被分隔开时
He was a man who, if had been properly supported, would have worked wonders. 他是一个本该创造出奇迹的人，如果当时给予适应的支持的话。

7) 当表示人的先行词由两个定语从句重叠修饰时(即双重定语从句)，第二个定语从句只能用who/whom引导，而不能用that。而且第二个定语从句的引导词不能被省略。
The only person I know who has a skeleton in the cupboard is George Carlton. 我所认识的唯一的在柜中藏骷嵝的人便是乔治. 卡尔顿。

当先行为人时，定语从句的关系代词一般情况下既可以用who/whom, 也可以用that，而且用who要比用that普遍。先行词为人时，还有一些情况下只能使用who而不能用that，这些情况可看《定语从句用who不用that的情况》一文。那么，有没有一些情况只能用that，而不能用who呢？答案是肯定的。下面就列举一些需要我们注意的情形。

1) 在疑问句中，如果开头的疑问代词是who，为了避免重复，定语从句宜使用that引导而不用who, 如:
Who is the hero that must thus be sacrificed? 谁是需要作出牺牲的英雄呢？
Who is the scientist that first discovered radium? 首先发现镭的科学家是谁？

2) 当先行词为疑问代词who, which时，如:
We all realized who that remark was aimed at. 我们都知道那话是对谁而言的。
Which of us that knows something about physics does not know this? 我们中但凡知道点物理知识的人哪一个不懂这个？

3) 当关系代词在定语从句中作表语或宾语补足语时，定语从句也不用who引导，而用that, 或者省略关系代词。
He is no longer the man that he was. 他已经不是过去的他了。(先行词在定语从句中作表语）
He is not the fool (that) you thought him. 他不是你想像中的那个傻瓜。 (注：这条句子中 the fool 在定语从句中作宾语补足语，即 thought him the fool)

4) 当先行词同时包含人和物时
The bike and its rider that had run over an old man were taken to the police station. 撞倒老人的车和事主已被带到警局。

当先行为人时，定语从句的关系代词一般情况下既可以用who/whom, 也可以用that，而且用who要比用that普遍。先行词为人时，还有一些情况下只能使用who而不能用that，这些情况可看《定语从句用who不用that的情况》一文。那么，有没有一些情况只能用that，而不能用who呢？答案是肯定的。下面就列举一些需要我们注意的情形。

1) 在疑问句中，如果开头的疑问代词是who，为了避免重复，定语从句宜使用that引导而不用who, 如:
Who is the hero that must thus be sacrificed? 谁是需要作出牺牲的英雄呢？
Who is the scientist that first discovered radium? 首先发现镭的科学家是谁？

2) 当先行词为疑问代词who, which时，如:
We all realized who that remark was aimed at. 我们都知道那话是对谁而言的。
Which of us that knows something about physics does not know this? 我们中但凡知道点物理知识的人哪一个不懂这个？

3) 当关系代词在定语从句中作表语或宾语补足语时，定语从句也不用who引导，而用that, 或者省略关系代词。
He is no longer the man that he was. 他已经不是过去的他了。(先行词在定语从句中作表语）
He is not the fool (that) you thought him. 他不是你想像中的那个傻瓜。 (注：这条句子中 the fool 在定语从句中作宾语补足语，即 thought him the fool)

4) 当先行词同时包含人和物时
The bike and its rider that had run over an old man were taken to the police station. 撞倒老人的车和事主已被带到警局。