which引导的定语从句用法如下：
一、which可引导限制性定语从句，用于指代物，一般在从句中作主语或宾语。
1、The song which was played on the TV is my favorite.电视上播放的那首歌是我的最爱。
2、I saw the letter which came yesterday.我看到了昨天寄到的信。
3、The movie which we watched was fantastic.我们看的电影很好看。
二、which引导限制性定语从句时，在从句中作宾语时，which可省略。
1、The movie (which)we watched was fantastic.(which)
2、This is the book (which)you asked for.(which)
三、which在限制性定语从句中作介词宾语时
该介词可以置于从句句末，也可以提前至which前，置于定语丛句之首，此时，which不可省略（置于从句之首较为正式）。
1、This is the book(which)you asked for.(which可省)
2、This is the book for which you asked.(此处which前面有介词for,所以不可省略）
四、which可引导非限制性定语从句
非限制性定语从句，用于指代主句的一部分或整个主句，一般在从句中作主语、宾语。（非限制性定语从句，是起补充说明的作用，是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开。
1、Water,which is a clear liquid,has many uses.水是一种透明的液体，有许多用途。
2、The bag,which I bought yesterday,is too expensive.这个包太贵了，我昨天买的这包。