A composite cooling system , comprising an indoor air duct and an outdoor air duct that are independent of each other, wherein the indoor air duct and the outdoor air duct intersect in a heat exchange area of the composite cooling system ; a first-stage heat exchanger core , a second-stage heat exchanger core , and a first side air duct are disposed in the heat exchange area , the heat exchange area is constructed as a part of the outdoor air duct , and the first-stage heat exchanger core , the first side air duct , and the second-stage heat exchanger core are sequentially arranged along a flow direction of the outdoor air duct ; an inner cavity of the first-stage heat exchanger core and an inner cavity of the second-stage heat exchanger core each are constructed as a part of the indoor air duct ; and the first side air duct is configured to permit air exchange between the heat exchange area and a region outside of the composite cooling system , wherein the first side air duct is configured to permit air in the outdoor air duct to flow from the first-stage heat exchanger core to the first side air duct , mix with air in the first side air duct , and flow from the first side air duct to the second-stage heat exchanger core ; wherein the indoor air duct comprises an air inlet section and an air return section , in a flow direction of the indoor air duct , the air inlet section is located at a front end of the heat exchange area , the air return section is located at a rear end of the heat exchange area , the first side air duct further communicates with the air inlet section and the air return section , a first air valve is disposed between the first side air duct and the air inlet section , a second air valve is disposed between the first side air duct and the air return section , and the first side air duct is also constructed as a part of the indoor air duct . a first-stage heat exchanger core , a second-stage heat exchanger core , and a first side air duct are disposed in the heat exchange area , the heat exchange area is constructed as a part of the outdoor air duct , and the first-stage heat exchanger core , the first side air duct , and the second-stage heat exchanger core are sequentially arranged along a flow direction of the outdoor air duct ; an inner cavity of the first-stage heat exchanger core and an inner cavity of the second-stage heat exchanger core each are constructed as a part of the indoor air duct ; and the first side air duct is configured to permit air exchange between the heat exchange area and a region outside of the composite cooling system , wherein the first side air duct is configured to permit air in the outdoor air duct to flow from the first-stage heat exchanger core to the first side air duct , mix with air in the first side air duct , and flow from the first side air duct to the second-stage heat exchanger core ; wherein the indoor air duct comprises an air inlet section and an air return section , in a flow direction of the indoor air duct , the air inlet section is located at a front end of the heat exchange area , the air return section is located at a rear end of the heat exchange area , the first side air duct further communicates with the air inlet section and the air return section , a first air valve is disposed between the first side air duct and the air inlet section , a second air valve is disposed between the first side air duct and the air return section , and the first side air duct is also constructed as a part of the indoor air duct . <EOS>