keep doing,keep on doing这两个词组均用来表示“不断做”的意思,但在涵义上有所不同.
keep doing和keep on doing都可表示“不断（老是）做某事”的意思,强调动作连续不断,每隔一会儿发生,这时两者可以换用.不同的是keep doing中的doing是动名词,作宾语.例如：John always kept (on) asking questions.约翰总是问个不停.News of successes keeps (on) pouring in.捷报频传.
keep doing还可表示连续不断的动作或持续的状态.keep on doing则没有这种用法.例如：We kept working in the fields in spite of the rain.尽管下雨,我们还是坚持在地里干活.Why do the dogs keep barking?这些狗为什么不停地叫?
keep up：
坚持不懈