In order to study the changes of vehicle dynamic response and tire dynamic load under different road levels, the time domain model of random road surface and the transfer function between four wheels and road surface were established by using filtered white noise method, and the dynamic response of vehicle on random uneven road surface was simulated. On this basis, considering the damping characteristics of the suspension system, the vehicle dynamics model of 14 degrees of freedom is established. The response of vehicle pitch Angle, roll Angle and tire dynamic load with road grade was studied. The results show that the dynamic response of vehicle state quantity fluctuates with the increase of road roughness, resulting in the gradual decrease of ride comfort and stability. Through the data analysis of vehicle state quantity and vertical force, it can be seen that the constructed vehicle model can reflect the vehicle state response under various road conditions, which provides a theoretical basis for the subsequent research of vehicle-road coupling.