how to get into Wangfujing if my flight arrives at 1 am in Beijing?

Yes, the airport shuttle bus line 2 is still in operation at that time.
So you can take that bus line to reach its terminal at Xidan and then change to take a taxi to your destination in Wangfujing.
Hope it helps you.

hi cara,

thanks for the info, btw, how can i get info about shuttle bus?

What do you wanna know?
About line 2 has daytime line and overnight line. The overnight line operates from 00:00 till the arrival of the last flight, with the interval less than half an hour. It costs CNY16 per person. At this link, you can find the infor about shuttle buses:
https://www.travelchinaguide.com/cityguides/beijing/transportation/airport-shuttle.htm