Abstract: Taking the rail pads of the thermoplastic polyurethane elastomer (TPEE) for example, the nonlinear curves between the static loads of TPEE rail pads and their corresponding compressed deformation were plotted by a universal testing machine. A rail-fastener finite element model used for the nonlinear static analysis was established to calculate the compressed deformation of rail pads and their corresponding static stiffness under the static vehicle weight and the preload of the rail fastener. Finally, the vertical vehicle-track coupled model was applied to investigate the influence of the constant stiffness, the frequency-dependent stiffness, the amplitude- and frequency-dependent stiffness of TPEE rail pads on the frequency-domain random vibration responses of the vehicle-track coupled system. Results indicate that the static stiffness of TPEE rail pads nonlinearly increases with the increase of their compressed deformation, and the static stiffness of TPEE rail pads ranges from 19.1 kN/mm to 37.9 kN/mm under 1/8 vehicle weight of 80 kN and rail fastener' preloading of 20 kN, with an average approximately equivalent to the hypothetically linear constant stiffness of 26.7 kN/mm in the national standard. Additionally, compared with the amplitude- and frequency-dependent stiffness of TPEE rail pads, their hypothetically linear constant stiffness leads to a severe underestimate of the random vibration levels of wheel-track coupled system at frequencies of 65 Hz~150 Hz. Thus, only if there are polymer materials with strong nonlinear stiffness in the vehicle-track coupled system, it is necessary to comprehensively consider its amplitude- and frequency-dependent stiffness; otherwise, it is difficult to accurately predict the frequency-domain responses of both the wheel-track coupled vibrations and the train-induced environment vibrations.