What's the easiest way from the great wall (Mutianyu or Badaling) to Beijing Capital Airport T2?

From Badaling Great Wall: Take bus no.877 and get off at Deshengmen Bus Stop. Then take metro line 2 to Dongzhimen Station. After arriving, take Airport Express to the airport. The duration is around 2 hours.

From Mutianyu Great Wall: Take bus no. h23, h24, h35, or h36 from Mutianyu Roundabout to Huairou North Avenue first. Then take bus no.916 Express and get off at Dongzhimen Bus Stop. Then you can also take the Airport Express to PEK. The whole way takes around 2.5 - 3 hours.