It is a tour bus and direct bus line to Mutianyu from Dongzhumen Transport hub. Bus 916 also at Dongzhimen can take you to huairou first and then you have to take a cab to The great Wall. Good Luck~

Thankyou for your reply, but istill don't know which bus to catch, how do i know it's the fast bus to mutianyu ? is there a special sign on the bus ? i have read many articles when people get to Dongzhimen that it's very confusing and they don't know which bus to get on, more information is greatly appreciated on location and times etc and how long this bus will take ?
many thanks
Joy

It is not easy to say clear, Mrs Barry. When I tried to find bus 919 bus to Badaling, there are 919快，919支... So, The bus station of 916 and 936 at Dongzhimen is not the bus station you see next to Dongzhimen Subway Station. You should walk about 100 meters and experience tells that even they are close, but no easy to find. So, take those bus from the city center 401、404、123、106、107, you can get to Dongzhimen Station of 916 and 936 directly. Yes, not all bus 936 runs to Mutianyu. So, ask people around there or the ticket seller. Or take either of these two buses to Huairou Bus Station. Then shift Huairou-Mutianyu bus after that.