The invention relates to the field of engine cooling systems and aims at providing a double-loop cooling system and method for an engine. The double-loop cooling system for the engine comprises a cylinder block water jacket and a cylinder cover water jacket, and a main water pump; the cylinder cover water jacket comprises an upper cylinder cover water jacket and a lower cylinder cover water jacket, the two of which are connected with the main water pump; the double-loop cooling system for the engine further comprises an engine oil cooler connected in series with the cylinder block water jacket, a radiator connected with the main water pump, a cylinder cover thermostat connected with the upper cylinder cover water jacket and a lower cylinder cover water jacket, a cylinder block thermostat connected with the cylinder block water jacket and the radiator, an expansion tank connected with the main water pump, a first degassing valve connected with the upper cylinder cover water jacket and the expansion tank, a second degassing valve connected with the main water pump and the expansion tank, and a third degassing valve connected with the cylinder cover thermostat and the expansion tank; a water temperature sensor is arranged at an outlet of the lower cylinder cover water jacket. The double-loop cooling system for the engine is good in dynamic property, economical efficiency and discharge property of the engine, and is further capable of prolonging the service life of the engine.