Abstract: The dynamic analysis model of a simply-supported beam under a vehicle modeled as a wheel-spring- damper-sprung mass is established, and the motion equations are derived. Using the vertical accelerations of the vehicle and its spectra, the fundamental frequency of the bridge is identified. The influences of parameters, such as bridge damping, vehicle, spring stiffness, damping ratio of vehicle mass to bridge mass, vehicle moving speed and acceleration, and bridge surface roughness, are studied. The main conclusions are drawn from an example: bridge damping does not affect the accuracy of frequency identification; better accuracy is achieved for smaller vehicle speed and smaller ratio of vehicle mass to bridge mass; the influence of bridge surface roughness is significant; the varying speed of the vehicle does not obviously affect the identification accuracy.