For the booming noise reduction by vibration mode control, structural and acoustic analyses or optimization procedure have been studied. For obtaining know-how to reduce booming noise, it is necessary to understand the mechanism of vibration phenomenon, and then to simplify the phenomenon. In this paper, it is presented that the booming noise should be reduced by using the simplification of panel vibration mode of vehicle body.Simplification is obtained by considering that panels are forced and vibrated by the body frame of the vehicle, and that panel vibration is decided by frame movement and stiffness and mass distribution in the panel. The simplification about panel vibration control by the appropriate mass and stiffness distribution is confirmed by using floor vibration. By appropriately controlling the stiffness distribution in the dash panel, booming noise caused by the dash panel vibration was reduced.