The formula to calculate the natural frequencies of vehiclebridge coupled system was established. Changes of the various steps natural frequencies of the coupled system with position ratio and stiffness ratio and the fundamental frequencies with speed and acceleration of the vehicle were researched. The results of numerical examples show that the natural frequencies of coupled system are related, not only to the location ratio but also to the stiffness ratio. The speed and acceleration of vehicle to the fundamental frequencies of coupled system produce different effects. Sometimes there will be bigger error if the natural frequencies of bridge are used instead of the natural frequencies of coupled system.