The invention provides a method for defrosting an air conditioning system. The air conditioning system comprises an indoor heat exchanger, throttle devices, an outdoor heat exchanger, a four-way valve, a compressor, a bypass circuit branch and a junction main circuit which are arranged on refrigerant circulation paths in a heating mode, wherein the compressor is connected with the indoor heat exchanger and the outdoor heat exchanger through the four-way valve; a heat accumulator is arranged on and connected with the compressor; the bypass circuit branch is connected between the four-way valve and the outdoor heat exchanger; and the junction main circuit is connected between the throttle devices and connected with the compressor by the heat accumulator. During defrosting, a refrigerant flows out of the compressor and passes through the four-way valve for bypassing, a part of the refrigerant enters the outdoor heat exchanger for defrosting through the bypass circuit branch, the other part of the refrigerant enters the indoor heat exchanger for heating, after heat exchange, the two parts of the refrigerant are subject to throttling, flow into the junction main circuit, enter the heat accumulator for heating, and then return to the compressor, so that the circulation is completed. The two parallel refrigerant circulation paths are formed in a defrosting state, so that the defrosting and continuous heating can be ensured at the same time.