英语中主从复合句是由一个主句和一个或一个以上的从句构成。
区分主句和从句主要会识别引导从句的连词，因为从句通常由连词引导。
例如：After you finish your homework, you can go out to have fun.在这句话中，after是连词，它必定引导从句，所以After you finish your homework是时间状语从句。主句就是：you can go out to have fun.
又如：The boy who has a basketball in his hands is my brother.在这句话中，who是连词，所以who has a basketball in his hands是在主句中作定语成份，修饰前面的名词boy的定语从句了。主句则是：The boy is my brother.
