Settlement difference of tunnel-bridge section results in the bump when vehicles pass, which reduces driving comfortableness. In this study, the process of vehicle passing tunnel-bridge section was regarded as a forced oscillation with certain initial conditions. Considering vehicle rotation and overturn in longitudinal direction, a dynamic model of vehicle-road was established, and a vibration equation was given. And the driver acceleration and impact force to road with various influencing factors were solved with Laplace transform. The result shows that the acceleration and force are influenced significantly by settlement difference and vehicle load, while the vehicle speed has little effect on them.