Based on the current study of planetary roller screw(PRS), a summary of how to match the main parameters of the PRS is obtained. A mathematic model for contact analysis is developed, where series of equivalent balls are used to replace the rounded profile of the roller. At the same time, the formula of axial contact deformation of the PRS is derived. Then a simplified finite element model of the PRS is established and the contact analysis is conducted by FEA. The FEA results and the theoretical ones agree well with each other, so the accuracy of the calculation method and the validity of the equivalent method are verified.