I will be arriving at Beijing international Airport at 8.30pm.

You may get the the last airport bus line 10 Wangfujing Jinbao Street Line at 21:00 and you can get off at the final stop and walk about 2 minutes to the hotel.
If you cannot catch the last bus, you can take the airport bus West Bus Station Line and get off at Ciqikou and get on the metro line 5 and get off at Dengshilou. Then walk about 4 minutes to the hotel.