The vehicle riding comfort has become one of important factors of vehicle quality and receives more increasing attention. The driving smoothness of vehicles has immediate influence on the riding comfort of vehicles. In this study, the mechanical model and mathematics model of the 1/2 five degrees of freedom of a vehicle were established, as well as the pseudo- excitation model of road conditions for the front wheel and the rear wheel. By the pseudo- excitation method, the equations of the transient response and the power spectral density were established. After numerical simulation to vehicle vibration response of uneven driving, the results show that the pseudo- excitation method is more convenient than the traditional method and effectively solves the smoothness computation of vehicles while the pseudo- excitation method is used to analyze vehicle vibration under non-stationary random vibration.