The human body is simplified as the parallel dynamic model and the vehicle as the seven-freedom vibrating model. The road is supposed as the Euler Beam on the Kelvin base. And then base on the compatibility deformation condition and the interaction force between the road and the vehicle, the dynamic functions of the body-vehicle-road coupled system are derived. The functions are been divided and solved with mode synthesis method and New-mark method. The process while the vehicle is running on the road is simulating, and the riding comfortable is analyzed with the synthetic comfortableness. It proffers the thereunder that the comfortableness can evaluate road roughness. And also the effects of the vehicle parameters, vehicles velocity, road surface class and the amount of passenger on the vibration of the system are also analyzed.