is it possible to go the great wall from the beijing international airport? If so, by train or bus?

Romero, there is no direct bus from the airport to the wall. You either take a taxi or use the airport shuttle bus and then change bus to visit the wall. If you rent a taxi, a round trip costs at least CNY800.

If you use public transportation means, you need to take airport express to Dongzhimen, change subway line 2 and get off at Jishuitan Station. Then you need get out from Exit A and walk to Deshengmen Arrow Tower. There you can take no.877 or 919 to the wall.

Or you can try to rent a car and a driver on this website. You can find Car Rental on the top of the page. It costs 139 usd.