Please advise how do I go summer palace from mutianyu great wall?

From the great wall, hire a car to Huairou North Street to take the bus No. 916 to Dongzhimen. At Dongzhimen subway station, you can take the subway line 2 to Xizhimen station, where you can transfer to line 4 to Beigongmen Station. Take the Exit A1, and walk about 420 yards, you will reach the entrance of the palace.