動詞do在句中的作用可以概述為四句十二字："做"實義，助動詞，替前文，強語氣。

作用一：實義do

do作實義動詞時，有do, does, did, done, doing五種形式，還有及物、不及物之分。如：

1. vt. "做;研究;整理;完成"。如：

①The old man does an hour of sport every day.

②She did her homework at home last night.

③Mother was doing the cooking when I reached home.

④Have you done the exercises yet?

2. vi. "行動;工作;進展;足夠"。如：

①Kate does very well in her Chinese.

②How do you do?

③Well done!

④That will do.

作用二：助動do

do作助動詞時，只有do, does, did三種形式，無詞義，限用于含行為動詞的一般現(xiàn)在時和一般過去時兩種時態(tài)的否定句和疑問句中。如：

①They don’t have any tickets for tonight’s concert.

②Kate stayed at home last night, didn’t she?

③How many books does the library have?

④She doesn’t do the washing in the evening.

作用三：替代do

為避免動詞的重復，使語言簡練，常以do, does, did替代前文所用的行為動詞。如：

①Tom runs much faster than you do.

②-Lucy, can you get some more tea, please?

-Sure. I’ll do it right away.

②-Who broke the cup?

-Mimi did.

③-I like bananas.

-So does he.

作用四：語氣do

為突出感情色彩，do常用于祈使句、強調句和倒裝句中，以加強語氣。如：

①Do be careful.

②Don’t tell a lie.

③He did come.

④-You often go to the park.

-So we do.