A simple quarter-vehicle model with two freedom degrees was founded on the basis of vehicle-road interaction,and the pavement surface roughness(PSR) was considered as excitation causes.The power spectral density(PSD) of the roughness of the road was described.The stochastic vibration theory was used to analyze the stochastic dynamic pressure of vehicle on rough pavement.Example analysis shows that the dynamic load coefficient increases along with the increase of vehicle velocity and PSR.Dynamic load coefficient is the important parameter reflecting the stochastic dynamic pressure.