倒计时的英语是count down。
例句：
1、现在开始圣诞节倒计时。
The countdown to Christmas starts here.
2、开始倒计时之前还有3件事要做。
There were three more things to do before countdown.
3、她已经在对这一重大日子倒计时了。
She's already counting down to the big day.
4、诺丁山狂欢节已经进入了最后几个小时的倒计时。
The countdown to the Notting Hill Carnival is in its final hours.
5、美国航天飞机的发射已于今天晚些时候开始进入倒计时。
The countdown has begun for the launch later today of the American space shuttle.
