动名词是动词的一种非谓语形式，由动词原形加-ing构成，它在句中起名词的作用，可以在句子中用作主语、表语、宾语、宾语补语、状语和定语。

1、 动名词作主语

Walking is good exercise. 走路是很好的运动

Seeing is believing. 眼见为实。

Smoking may cause cancer. 吸烟可能导致癌症。

Coming to Hangzhou by train takes about 16 hours. 乘火车到杭州要16个小时。

Swimming develops the muscles. 游泳可以发展肌肉。

通常为了避免句子主语过于冗长，用it作形式主语。如：

It's nice talking with you.

和你谈话很高兴。

It's no use arguing with him.

跟他争论没用。

It is no use sending him over. It’s too late already. 派他去没用，已经太晚了。

It was very difficult getting everything ready in time. 要把一切按时准备好很困难。

“There + be + no + -ing”结构，如：

There is no joking about such matters. 这种事开不得玩笑。

There is no harm in doing so. 这样做没有害处。

There is no denying the fact that the new method has greatly raised labour productivity.

不容否认新方法大大提高了劳动生产率。