Based on the meshing principle of Planetary Roller Screw (PRS), the meshing clearance of screw pair is minimized by taking the half of thread angle, and the pitch diameter tooth thickness, e, as the optimization variables. Optimal structural parameters are obtained by using optimization module of the software Matlab. The 3D model of PRS structures are established with Solidworks and the finite element contact analysis is carried out with Ansys. The contact deformation and stress distribution are calculated among screw, rollers and nut. The results can be used for PRS design.