I'll be reaching Beijing Capital Airport at 23.00pm and there won't be any more express train.

According to your landing time, you can take the shuttle bus Xidan Night Line. The operating hours of this shuttle bus are from 24:00 to the last domestic flight arrival. The buses depart every 30 mins or once fully seated. The ticket fare is CNY 24 per person.
Or at that time, you can also take a taxi from the airport. Take Wangfujing Street as an example, the cab fare from the airport is CNY 110-120.