The open-cell polyurethane foam has a significant influence on the dynamic response of the Seat-occupant Coupling System (SoCS). Hardness, as an important property of foam, significantly impacts the compliance of human body support. Therefore, it is necessary to study the effects of varying foam hardness on the vibration transmitted to the human body. In this study, the effects are investigated by combining the test and simulation. In the test, the vibration transmission characteristic is measured and analyzed using Transmissibility, Seat Effective Amplitude Transmissibility (SEAT) value, and Weighted Root-Mean-Square value (W-RMS). In addition, the properties o dynamic stiffness and damping are also discussed. In the simulation, combined with the test results of dynamic stiffness/damping, a three-degree-of-freedom (3-DOF) model of SoCS is established. Meanwhile, by introducing goodness of fit, the consistency of simulation and test results is evaluated and quantified. The results indicate that (1) With increasing foam hardness on the seat pan, the resonance frequency almost remains constant, and the transmissibility associated with the resonance increases. (2) When the foam becomes harder, the damping characteristic also changes obviously, which causes that the vibration of SoCS attenuates faster and the SEAT value and W-RMS also go smaller. (3) Moreover, both the dynamic stiffness and damping decrease with the increasing foam hardness, which reveals they are consistent in this case. (4) The simulation results are in good agreement with the test results, which further indicate the validity of the proposed 3-DOF model.