The configuration selection and parameter optimization of 6-PSS parallel mechanism with planar platform were studied. According to the characteristics of 6-PSS parallel mechanism with planar platform, the essence of configuration selection was to solve layout problem of linear guides on base, and four typical configurations of 6-PSS parallel mechanism with planar platform were given. Firstly, the inverse kinematics model was established and the Jacobian matrix was derived and verified by ADAMS simulation. Secondly, in order to observe the shapes and ranges of workspace, workspace maps and their projections were drawn. Similarly, dexterity distribution diagrams were drawn to intuitively observe the distribution of dexterity. In addition, their workspace volume and global dexterity were calculated. By comparing the reachable workspace range, volume, dexterity distribution and global dexterity value of the four configurations, it was concluded that configuration Ⅲ had better performance in the above aspects. Then, for configuration Ⅲ , for the purpose of analyzing the effects of structural parameters on its workspace and dexterity. The projections of workspace corresponding to different structural parameters were drawn, and the workspace volume and the global dexterity corresponding to different structural parameters were calculated. The results showed that the workspace volume and global dexterity were positively correlated within a certain range of structural parameters, and its reasons were analyzed. Finally, the workspace volume was optimized and the optimal structural parameters were obtained. The workspace volume and global dexterity were significantly improved after optimization. And error analysis of the optimized mechanism was carried out. The research result had a strong guiding significance and reference value for the design of 6-PSS parallel mechanism with planar platform.