The present invention relates to a cooling system for an engine inside a power generator, in the field of the power generator, which mainly includes a cool air suction hood, an engine housing side cover, an engine housing, a cool air cooling fan, an exhaust pipe; the cool air suction hood is jointed to the engine housing side cover, the left air guide plate and the right air guide plate on the upper of the engine secured to the engine housing, thus form two main cooling and ventilating chambers A and B on the left and right upper portion of the engine. An engine bottom air guide plate is secured to the bottom of engine housing side cover and forms the bottom cooling and ventilating chamber C of the engine with the side cover and an engine crank case rear cover. The engine crank case rear cover, the above-mentioned members, a heat insulation chamber body, a sealing ring and a heat insulation chamber rear hood form a double chamber cooling means of the secondary cooling cycle chamber D. The jointing surfaces of the cooling system are increased. The requirements for cooling the engine are more reasonable so that the portions of the engine with high heat are ensured to be timely cooled and provide a highly cooling effective for the engine.