The invention relates to a cooling system and a method for an electrical appliance unit of a power device, which are characterized in that a liquid pump, a liquid cooling cavity for the electrical appliance unit and a radiator are connected in sequence through a liquid flowing pipe to form a liquid cooling loop; an engine blower and the radiator are arranged oppositely; a primary filter screen, an air cooling cavity for the electrical appliance unit and an air cleaner are connected with an engine in sequence to form an air cooling path. The engine drives a liquid pump, so that cooling liquid flows in a circulative way in the liquid cooling loop; meanwhile, the blower blows at the radiator to bring away the heat in the cooling liquid, thereby realizing liquid cooling for the electrical appliance unit; at the same time, when the engine inhales air, the pumping function of a piston inhales the cold air outside into the air cooling path from the primary filter screen, and when flowing through the air cooling cavity for the electrical appliance unit, the cold air absorbs heat from the surfaces of the electrical appliance unit and the liquid cooling cavity and enters a cylinder of the engine to participate in the burning process. By adopting the system of integrating the air cooling and the liquid cooling, the device and the method of the invention can enhance the cooling effect for an electrical appliance unit that gives out heat, improve the working environment of the electrical appliance unit and improve working efficiency.