An interactive game system has a main apparatus and a wireless controller. The main apparatus has three ultrasonic receiving modules. The wireless controller has an ultrasonic sending module. The three ultrasonic receiving modules receive ultrasonic signals sent by the ultrasonic sending module, and the main apparatus calculates the position of the wireless controller. When the wireless controller is moved, the main apparatus obtains a plurality of coordinate values indicating the motion track of the wireless controller. In this case, an electronic device shows the movement of the wireless controller on a display device by monitoring the coordinate values.