连系动词(link v.)是一种本身有一定的意义，但不能独立做句子谓语的动词，需要在它的后面加上表语一起构成"系表结构"。最常见的系动词be(是)，但有些感官动词和有些表示变化的动词也可作连系动词。其用法特点如下：一、be用作连系动词，后常加形容词、数词、副词、名词、介词短语等作表语。例如：She is beautiful.
He was thirteen last year.Is your mother in? No, she's out.　　My father is a doctor.　　The bag isn't on the desk. It's in the desk.二、常见感官动词用作连系动词及常与其搭配的形容词。例如：The school looks so beautiful. 学校看起来很美。The plan sounds nice. 这个计划听起来不错。The meat smells terrible. 这肉闻起来很难闻。The milk tastes sour. 牛奶酸了。She feels a little nervous.她感到有点紧张。三、表示变化的连系动词及常与其搭配的形容词。例如：His face is turning red. 他的脸变红了。Our country is becoming stronger and stronger. 我们的国家正变得越来越强大了。When summer comes, it is getting hotter and hotter. 当夏天到来时，天气变得越来越热。四、表示感觉和表示变化的连系动词的否定、疑问以及时态变化的形式均类似于行为动词。例如：They don't look well.The music sounds nice, doesn't it?　Did he feel excited at the news? Beijing is becoming more and more beautiful.