The invention belongs to the technical field of air conditioners, and particularly relates to an air conditioning unit and a control method thereof. The problem that when an existing air conditioning unit operates in a low-temperature environment, the heat exchange effect becomes poor due to the fact that the air return temperature is too low is solved. Therefore, the air conditioning unit comprises a refrigerant circulation system, a regenerative branch and a regenerative heat exchanger, the refrigerant circulation system comprises a refrigerant circulation pipeline, an indoor heat exchanger, a four-way valve, a gas-liquid separator, a compressor and an outdoor heat exchanger, and the indoor heat exchanger, the four-way valve, the gas-liquid separator, the compressor and the outdoor heat exchanger are arranged on the refrigerant circulation pipeline; based on the arrangement of the regenerative branch and the regenerative heat exchanger, a medium-temperature medium-pressure refrigerant can be used for heating the refrigerant before entering the gas-liquid separator so as to increase the return gas temperature, and the temperature of the refrigerant in the regenerative branch is further increased through the refrigerant flowing through an outdoor coil pipe; and in addition, the communicating time of the regenerative branch and the refrigerant circulation system is accurately judged according to the temperature of the outdoor coil pipe and the return air temperature, so that the air conditioning unit can complete defrosting in the shortest time.