▲the day after tomorrow 前面通常不用介词 on。比如《牛津英语用法指南》指出：在yesterday, the day before yesterday, tomorrow 或 the day after tomorrow 前面一般不用 at / on / in。如：

What are you doing the day after tomorrow? 后天你干什么?

更多例句如：

I’ll see you the day after tomorrow. 我们后天见。

We leave the day after tomorrow. 我们后天离开。

I’m leaving the day after tomorrow. 我打算后天动身。

“I’m starting the day after tomorrow, mother,” he said. 他说：“妈妈，我后天动身。”

▲但是，若一定要在 the day after tomorrow 前面加上介词 on 也不算错（但远不如省略on普通）。比如下面一句出自《剑桥高级英语词典》的句子就用了介词 on：

There’s a good film on the day after tomorrow. 后天有一部不错的电影。