on and off

(also off and on)

If something happens on and off during a period of time, it happens sometimes.

时断时续地;间歇地

I've had toothache on and off for a couple of months.

我的牙断断续续疼了几个月。

He studied for his degree on and off for 75 years.

他断断续续学习了75年的时间。

It rained on and off all day.

雨断断续续地下了一整天。