In order to explore the best nonlinear passive vibration isolation mechanism, the stiffness of the nonlinear passive vibration isolation system of roller and spherical-contact is modeled and analyzed. And the ADAMS dynamic model of the system is established. Parameter analysis is carried out, influences of the main parameters on the performance is studied, and the main parameters which will be adjusted when the isolated mass changes is found. The research results are helpful to the nonlinear vibration isolator and non-road vehicle seat suspension design.