The invention discloses an air-conditioning system which comprises a compressor, a first outdoor heat exchanger, an indoor heat exchanger, a throttling assembly, a four-way valve, a cold storage device and a three-way valve. The cold storage device comprises a cold storage box containing a cold storage agent, a second outdoor heat exchanger and a third outdoor heat exchanger, wherein the second outdoor heat exchanger and the third outdoor heat exchanger are contained in the cold storage box; the first end of the three-way valve is connected with the four-way valve through the third outdoor heat exchanger, the second end of the three-way valve is connected with the four-way valve, and the third end of the three-way valve is connected with an exhaust opening of the compressor; and the second outdoor heat exchanger is connected between the throttling assembly and the indoor heat exchanger. The invention further provides a control method of an air-conditioner. According to the air-conditioning system and the control method, when the first end and the third end of the three-way valve are communicated, a refrigerant exhausted from the exhausting opening of the compressor absorbs the cold amount of the cold storage agent when passing through the third outdoor heat exchanger for reducing the temperature of the refrigerant passing through the third outdoor heat exchanger, the temperature of the refrigerant is reduced after the refrigerant passes through the indoor heat exchanger, the air return temperature of the compressor is reduced, the exhaust temperature of the compressor is further reduced, and normal running of the system is guaranteed.