英语动词什么时候加ing的规则

1、动名词。例：Swimming is good for health.

2、现在进行时。例：I am doing my homework.

3、动词并列。例：She stood here,reading a book.

4、动词前有部分介词。例：She is looking forward to seeing him.

5、有些动词加ing变为形容词。例 ：exhaust加ing为exhausting，此时词性由动词变为形容词。