1、以重读闭音节结尾，末尾只有一个辅音字母的动词，要双写这一辅音字母，再加-ing。例如：run-running, swim-swimming等。
2、以-al,-er,-ill结尾的动词，即使重音不在最后一个音节上，也要双写，再加-ing 如：travelling等。
可以加动词ing的
①及物动词。She likes drawing very much.；
②某些短语动词。 Mary is thinking of going back to New York.；
③ do+限定词（my, some, any, the等）+ -ing，表示“做…事”之意，如：We often do our cleaning on Saturday afternoon. Will you do any shopping on Saturday this afternoon?
④介词：Her sister is good at learning physics.；
⑤形容词worth, busy等：This book is well worth reading. –ing作宾语带有宾语补足语时，要用it作为形式宾语，而将作宾语的-ing后置，如：We found it no good talking like that. Do you think it necessary trying again?
