A new random vibration model of vehicle-bridge systems using pseudo excitation method (PEM) is proposed, based on the bridge modeled as beam elements and the vehicle modeled as two-degrees of freedom mass-spring-damper system. The responses of vehicle and bridge caused by road spectrum functions are researched based on the GB7031 spectrum, Wang spectrum and ISO spectrum, respectivley. The research covers the effect on vertical dynamic response of bridge, the sensitivity of bridge vibration due to vehicle speed and the dynamic responses of vehicle caused by road spectrum function. The results reveal the following conclusions: three road spectrums have the similarity vertical displacement root mean square (RMS) curve at mid-span; the resonance frequency appears at the bridge′s fundamental frequency; the vibration responses of vehicle caused by ISO spectrum change with vehicle speed weakly. However, the bridge dynamic responses caused by ISO spectrum show evident sensitivity in vehicle velocity. The dynamic response and resonance frequency of vehicle and bridge coupling caused by the GB7031 spectrum are approach to that of the Wang spectrum. The result of GB7031 spectrum is slightly greater than that of the Wang spectrum.