I am travelling to Beijing Badaling Hot Spring Resort. How far is it from The BJ Airport?

There is about 95km between by car.
From the airport, you can take the airport express to Dongzhimen Station and then change to local public subway line 2 to Jishuitan Station. Get out of the station, you can walk to the Deshengmen Bus Station, where you can easily find the bus line 919. So you can take that line to Guishuibe Road South (妫水北街南) and then walk along the Guishuibei Road to your hotel easily.