A vehicle network transmission method and a vehicle network transmission system are provided. The vehicle network transmission method comprises the following steps. A first transmission device transmits a data signal to a second transmission device. It is determined whether the second transmission device is located in a target area. If the second transmission device is located in the target area, then a geographic location of the first transmission device is retrieved and a transmission region of the first transmission device is calculated. It is determined whether all of the third transmission devices adjacent to the second transmission device in the target area are located in the transmission region. If all of the third transmission devices adjacent to the second transmission device in the target area are located in the transmission region, then the second transmission device does not continue forwarding the data signal.