May I visit Jinshaling from Beijing,and then continue to Chengde?

You may hire a taxi to the entrance of Jingcheng Highway and then wait for a coach to Chengde. But you can only get on bus when there are empty seats. The fastest way should be charter a private car all the way to Chengde.
Or, you may get back to city downtown area first, and then take a coach to Chengde from either Liuliqiao Bus Station or Sihui Bus Station.