"大吃一惊"的英文表达是"to be taken aback"或者"to be shocked". 这个短语有英语"back"和"aback"两个单词组成，它们都有"后面"的意思，而"to be taken aback"这个短语本意就是被吓得往后退一步。

下面是一些例句：

I was taken aback when I saw how much the bill was. 我看到帐单上的数目后大吃一惊。

She was shocked to learn that she had won the lottery. 她得知自己中了彩票后大吃一惊。

He was taken aback by her sudden outburst. 她突然的大叫声让他大吃一惊。