There are five D trains from Shanghai Hongqiao Train Station after 21:00 to Beijing South Railway Station, arrive at 7am or so. Then you swift to Subway Line 4 from Beijing South Railway Station to Xizhimen and then change to Line 2 for one stop only to Jishuitan. Then get out from Exit A and walk a bit back to find Deshengmen Gate. There are 919 bus to Badaling there. While getting back to Shanghai, you can alternatively go to Beijing Railway Station by subway Line 2 from Jishuitan. There are T trains to Shanghai Railway Station, arriving at noon. You need not to catch up the D trains at Beijing South Railway, for they are arriving at Shanghai Hongqiao Train Station, far away from the city center. You need to take subway to reach downtown area.