In a method for determining a shot position of a light gun on a display screen, a current image is captured by an image capturing device of the light gun. The method detects a screen area in the current image, calculates coordinates of an aimed point of the light gun on the display screen when the screen area has been detected, and transmits the coordinates of the aimed point of the light gun to a host computer so that a shot result of the light gun is displayed on the display screen by the host computer according to the coordinates of the aimed point of the light gun on the display screen.