高中英语定语从句详解定语从句三步：第一找出先行词；第二看先行词在定语从句中的语法功能（做主语、宾语或状语）；第三选择合适的关系词。
(1) 定语从句：在主从复合句中用作定语的从句叫定语从句。
定语从句一般紧接在先行词(antecedent)后面。
(2) 先行词：被定语从句修饰的成份。
先行词可以为一个词，短语，或整个主句。
(3) 引导定语从句的词叫关系词，分为关系代词和关系副词。
关系词的作用：1) 引导定语从句，连接主句和从句，相当于一个连词；2) 必在从句中作某个句子成份（可以做主语，宾语，表语，定语，状语）常用的关系代词: that、which、who、whom、whose、as (其中whose只能做定语,which和what也可以做定语)常用的关系副词（在从句中只作状语）: when、why、whereEx.) He was late .That's because he got up late..He got up late. That's why he was late.(表语从句)(the reason) why/for which he was late. (定语从句)比较：Here is so big a stone as no one can lift. （定语从句）Here is so big a stone that no one can lift it.（结果状语从句）There are occasions when joking is not permissible.●关系代词作介词宾语:关系代词在定语从句中用作介词宾语时, 介词可放于从句之首, 也可放于从句之末. 但以放于句首较为正式.（介词前置，必须注意不影响动词词组的含义。
关系代词who 和that 用作介词宾语时, 介词必须放在句末.）This is the book for which you asked.=This is the book (that/which) you asked for.This is the girl whom they are looking after. (介词after与look构成固定词组，不可前置。
look at, look for, look after, take care of等)当先行词为way时，定语从句常用that, in which,或how引导，that常可以省略。
way后的定语从句的引导词不用时较多。
但如果关系词在句中作主语或宾语时，则用which或that 引导。
如:This is the way (that) /in which I do such things.比较: Please do the experiment in the way （that/which）I have shown you.Ⅳ. 限制性定语从句与非限制性定语从句的区别：1. 形式上，非限制性定语从句往往用逗号隔开。
2. 语法上，非限制性定语从句一般不用that.3. 语义上，限制性定语从句与先行词关系紧密，起限定作用，如果去掉了这个定语从句，整个句子就不完整或者会改变意思；而非限制性定语从句与先行词关系不是很紧密，对先行词起补充说明或描述的作用。
This is the book I like best. 这就是我最喜欢的那本书。
Beijing, which has been China's capital for more than 800 years , is rich in cultural and historic relics. 北京是中国八百年之久的古都，它有着丰富的文化和历史遗产。
4. 翻译时，限制性定语从句可译为一句（较短的一般译为"的"字结构）；而非限制性定语从句可译为两句。
（见上句翻译）比较: He has a sister, who is a musician.He has a sister who is a musician.引导非限制性定语从句的关系代词，指人时用who, whom, whose , 指物时用which , whose; 关系副词when，where, why, etc.1. He studied hard at school when he was young, which leads to his success in his later life.2. Tom's father, who arrived just now, is a famous scientist.3. They set up a separate state of their own, where they would be free to keep Negroes as slaves.4. He was proud, which his brother never was.Ⅴ. 几个易混淆的关系代词的比较:●that & which:在定语从句中，which 和that 在指代事物时，一般可以互换使用，但并非在任何情况下都是这样，这里介绍宜用that, 而不宜用which 的情况.①先行词为不定代词,all,much,something,everything,anything,nothing,none,the one等,1.We should do all that is useful to the people .2.There's nothing that can be said about it .3.Do you mean the one that was bought yesterday?②先行词被only, any, few, little, no, just, very, one of等词修饰时。
1.The only thing that we could do was to wait.2.That's the very word that is wrongly used.The last place (that) we visited was the chemical works.You can take any (=whichever) seat that is free.I hope the little thing that I can do will be of some help to them.比较*This is one of the best novels that were published last year.*This is the only one of the best novels that was published last year.③先行词是序数词时或被序数词修饰时。
1.When we talk about Wuxi, the first that comes into mind is Tai Lake.2.This is the third film that has been shown in our school this term.④先行词是最高级或被最高级修饰时。
1.This is the best that can be done now.2.The most important thing that should be done right now is how to stop him from going on.⑤先行词既有人又有物，用which和who都不适合，这时宜用that. 如：1.The writer and his novel that you have just talked about is really well known .2.The rider and his bike that had run over an old woman were held up by the police.⑥被修饰词为数词时.1.Yesterday I caught two fish and put them in a basin of water .Now you can see the two that are still alive .⑦如果有两个从句，其中一个关系代词已用which ,另一个关系代词宜用that，以避免语言的单调或重复。
Edison built up a factory which produced things that had never been seen before.⑧疑问词是who或which，关系代词宜用that，以避免重复。
1. Which is the book that you like best?2. Who is the man that is standing at the gate?⑨主句是There be 结构，修饰其主句的定语从句宜用that 作关系代词. 如：1. There is still a seat in the corner that is still free.⑩被修饰成分为表语时，或者关系代词本身是定语从句的表语时,该关系代词宜用that .1. That's a good book that will help you a lot.2. My home village is no longer the place ( that ) it used to be .定语从句中宜用which而不宜用that 的情况:①当关系代词的前面有介词时.1.A zoo is a park in which many kinds of animals are kept for exhibition.2.Is this the room in which Mr. White lives?②在非限制性定语从句中.1.Crusoe's dog, which was are now very old, became ill and died .2.More and more people are beginning to learn English, which is becoming very popular in our country. (which指代主句)③在一个句子中有两个定语从句，其中一个定语从句的关系代词用了that, 另一个宜用which .1. Let me show you the novel，that I borrowed from the library which was newly open to us.2. At the station I bought some magazines that might help me to pass the time on the train and which I could pass on to others when I finished them.④当关系代词后面带有插入语时.1. Here's the English grammar which, as I have told you, will help improve your English.⑤先行词本身是that, 宜用which .What's that which she is looking at?⑥先行词是those+复数名词.A shop should keep a stock of those goods which sell best.(B) who & that:who 和that 指代人时，有些情况宜用who, 而不宜用that①先行词为anyone, anybody, those, all, one, ones, they, he, people时. 如：1.The person I want to learn from is the one who studies hard and works well.2.Anyone who (=Whoever) failed to come to the meeting yesterday must give his reason .3.Those who are not fit for their work should leave office at once4.I don't like the ones (= those ) who talk big.5.Persons who are quarrelsome are despised.②在There be 结构中，修饰主语的定语从句宜用关系代词who 指代人. 如：1.There is a gentleman who wants to see you .2.There are several students in our class who are still not sure about the use of attributive clauses.③当先行词有较长的后置定语时. 如：1. I met a foreigner in the park yesterday afternoon who could speak Chinese very well.④一个句子中带有两个定语从句，其中一个定语从句的关系代词是that ,另一个则宜用who, 以免重复. 如：1. The student that was praised at yesterday's meeting is the monitor who is very modest and works very hard .●as & which:as & which 引导非限制性定语从句的区别：①位置的不同：which 引导的定语从句只置于所限制的句子后；as 位置较灵活，也就是说as可置于所限制的句子前面；插在句子中或放在句子后。