This paper introduced basic concept and resolvent of nonlinear FEA, the analysis of intensity and stiffness of the rear leaf spring on SC1020 vehicle was carried out with contact nonlinear function of FEA program ANSYS, and the pre-stress distribution and pre-deformation after assembled were introduced , the stress distribution and deformation under different loads had also been presented. Thus we can calculate the mechanical and dynamic performance of leaf spring at the design stage. The result showed a great agreement with the test. It is convinced that the CAE (Computer Aided Engineering) technology can improve the design of vehicle suspension and the cost and time can be saved.