In order to solve the contradiction between reducing the natural frequency and ensuring the stiffness of the system in the design of the suspension seat, the inerter was applied to the suspension seat system. Several kinds of ISD (Inerter-Spring-Damper) suspension seat structure were modelled. By combining with human body model, the four degrees of freedom Human—Seat systems were established. The seat bench test was carried out for the purpose of identifying the parameters of the suspension seat and the human model. Under EM3 excitation, the isolation performance of the ISD structure S2 and S6 were analyzed. The results show that the parallel structure of the inerter, spring and damper is the most suitable structure for the suspension seat, especially for low frequencies. This structure has the characteristic of high pass filter, can reduce the natural frequency of the system and improve the comfort of the seat, significantly.