The method to simulate the low-frequency road noise to 100Hz is presented,and the measured road surface is used for input for the simulation.The transfer path analysis and panel contribution analysis are done for the low speed road noise problem of se-dan,the result shows that: Middle beam of roof have high contributions to the interior noise.The stiffness of middle beam is improved,and the problem of low speed road noise is resolved.The validity of the simulation is shown by the comparison of the simulation results with measured vehicle interior responses.