which 与 that 在定语从句中被称为关系代词，其区别如下：
that和which在从句里都可以做宾语和主语，做宾语时可以省略。但which能引导非限制性定语从句，that则不行。
需区分只能用that和只能用which的几种情况。
1、只能用that，不用which作为定语从句关系代词的情况
a)不定代词，如anything, nothing, the one, all, much, few, any, little等作先行词
There is nothing that I can do.
I mean the one that was bought yesterday.
b)先行词有the only, the very, the same, the last修饰
This is the very book that I want to find.
The last place that I visited was the hospital.
c)先行词为序数词、数词、形容词最高级时
This is the first composition that he has written in English.
d)先行词既有人，又有物时
He talked about the teachers and schools that he had visited.
2、不用that, 只用which的情况
a)引导非限定性定语从句时which
The tree, which is four hundred years old, is very famous here.
b)介词后用which
This is the room in which I was born.
扩展资料：
定语从句是由关系代词和关系副词引导的从句，其作用是作定语修饰主句的某个成分。
that和which区别如下：
1、that即可代表事物也可代表人，which代表事物；它们在从句中作主语或宾语，that在从句中作宾语时常可省略关系词，which在从句中作宾语则不能省略。
2、 which作宾语时，根据先行词与定语从句之间的语义关系，先行词与which之间的介词不能丢。
如果which在从句中作“不及物动词＋介词”的介词的宾语，注意介词不要丢掉，而且介词总是放在关系代词which的前边，但有的则放在它原来的位置 。
3、代表物时多用which，但在带有下列词的句子中用that而不用which，这些词包括all, anything, much等，这时的that常被省略。