1、以重讀閉音節(jié)結(jié)尾,末尾只有一個輔音字母的動詞,要雙寫這一輔音字母,再加-ing.例如：run-running, swim-swimming等.
2、以-al,-er,-ill結(jié)尾的動詞,即使重音不在最后一個音節(jié)上,也要雙寫,再加-ing 如：travelling等.
可以加動詞ing的
①及物動詞.She likes drawing very much.；
②某些短語動詞. Mary is thinking of going back to New York.；
③ do+限定詞（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介詞：Her sister is good at learning physics.；
⑤形容詞worth, busy等：This book is well worth reading. –ing作賓語帶有賓語補(bǔ)足語時,要用it作為形式賓語,而將作賓語的-ing后置,如：We found it no good talking like that. Do you think it necessary trying again?