<p>To solve the problem of continuous quasi-zero stiffness vibration isolation system on large-amplitude vibration, a novel quasi-zero stiffness isolator with a type of piecewise cam negative stiffness structure (QSI-PCNS) is proposed, which can suppress large-amplitude vibration while ensuring a better vibration isolation effect at low frequency. In this paper, the novel QSI-PCNS of vehicle seat suspension system is established. The approximate analytical solution for the steady-state response of the system under the harmonic excitation is obtained by using multi-scale method, and its accuracy is verified by numerical method. Also, the influences of excitation amplitude and damping on the vibration isolation performance are, respectively, discussed. Moreover, the simulation model is designed and the stability of the system is investigated based on the Lyapunov theory. Compared with other isolators, the results show that the suspension system can effectively suppress the low-frequency large-amplitude vibration, and the critical excitation amplitude and critical damping of the system are determined. The system has the best vibration isolation performance when the excitation amplitude is larger than the primary critical excitation amplitude and smaller than the secondary that. Meanwhile, as the damping value is greater than the critical damping, the vibration isolation effect of the system is significantly improved, and the absolute displacement transmissibility of the system remains basically unchanged as the damping value keeps increasing. It indicates that the critical excitation amplitude can be controlled by adjusting the damping ratio so that the nonlinear system can still have better vibration isolation performance under the larger excitation amplitude.</p>