If arrive nanning around 10pm, are there any buses I can take from wuxu airport to beihai?

No, there is no bus at that time. You are suggested to stay at the hotel nearby the airport for one night.
In the next morning, take airport shuttle bus line 2 to Jiangnan Bus Station first. There are lots of buses at this station that can take you to the city directly. The schedules are from 07:30 to 21:00 with the interval of 30 mins. The ticket fare is CNY 55 per person.

now there is the direct bus from Nanning airport to beihai eryun bus station , about 2.5 hours , RMB 100. Or you can take the shuttle us(around 50minutes , 20RMB) to Nanning dong Railway station, then go to beihai by train, about 1.5 hours , around 59RMB.