After simplifying the road surface of the transition section of the road and bridge with the bridge head deck, the analysis model of the vertical vibration system of the road when the vehicle passes through the deck is established. The displacement response, velocity response and acceleration response of the human-vehicle system when the vehicle gets off the bridge are solved and calculated by modal analysis method. The vibration characteristics of vehicles passing through the road and bridge sections were evaluated by using the built human-vehicle road system analysis model. Combined with the characteristics of highway alignment, the relationship between the differential settlement index of the transition section of the road and bridge and the slope difference, bridge deck slope, vehicle speed, load, length and other factors was determined, and finally the allowable slope difference of the transition section of the road and bridge should not exceed 0.4% from the functional point of view.