Going to Great Wall from Beijing airport

Which section of Great Wall do you want to visit?
Suppose you wanna visit Badaling Great Wall. I suggest you take Express Train to Dongzhimen Station, where transfer to subway line 2 and get off at Jishuitan Station from where you can easily walk to Deshengmen. At Deshengmen, you can catch bus no. 919 or 880 to reach the great wall directly.

If you refer to Mutianyu Section, upon your arrival at Dongzhimen by Express Train, you can take Tourism Bus No.867 at Dongzhimen Bus Station to Mutianyu directly in about 2.5 hours.

Do you refer to that the overnight transport to the Great Wall? If so, I'm afraid there is no such transport. If you mean the transport to the city center, from the airport, you can take the Night Line of Shuttle Bus line 2 to the downtown. It will not end its service until the arrival of the last flight.