Abstract: A 8 DOF vehicle model was built, and the inverse pseudo excitation method was used to work out the PSD of vehicle body vertical acceleration, the suspension dynamic deflection and the wheel relative dynamic load in the context of unknown spectral density of road excitation and known vertical vibration response-PSD of the wheel. A simulation program is designed using MATLAB to compare the ride comfort of the sure pavement with that of the unkown one. The results show that the method presented in this work is simple and practicable, which can solve the problem of settimg the road excitations and is worth of application in automobile vibration study.