A gear box structure for a toy gun includes a box, a trigger assembly, an elastic member, a push plate, and a stop piece. The push plate is provided with a stop end which is interfered with a stop strip installed on the stop piece, so as to create a resistant force between the push plate and the stop piece. When pulling the trigger, the trigger assembly will drive the elastic member to slide the stop end of push plate over the stop strip of stop piece, thereby forming a tightness and looseness feeling as if pulling a trigger of real gun.