Abstract: Problems regarding nonlinear natural vibration of pendulum spring under foundation displacement excitation are studied. The nonlinear natural vibration equation is found for the shock absorber system with the pendulum spring under foundation displacement excitation. The approximate solution of nonlinear natural vibration for the shock absorber system with the pendulum spring is derived by L-P method. Conclusion through calculation analysis is obtained: the amplitude and frequency of time-history curve for the shock absorber system with pendulum spring become smaller with the increase in the frequency of foundation displacement excitation,and the amplitude of time-history curve for the shock absorber system with pendulum spring will increase with the increase of the frequency of foundation displacement excitation the amplitude and the oblique angle of pendulum spring. At last comes the conclusion that the shock absorber effect of the shock absorber system with pendulum spring works better than shock absorber system with vertical installed spring.