The invention belongs to the technical field of heat pump units, particularly provides a heat pump system and a control method thereof, and aims to solve the problem that a conventional heat pump system is sufficient in heat supply. The heat pump system provided by the invention comprises a first heat exchanger, a heat exchange terminal, a water inlet pipeline and a water outlet pipeline, whereinthe water inlet pipeline and the water outlet pipeline are arranged between the first heat exchanger and the heat exchange terminal; a first electromagnetic valve and an electric auxiliary heating device are arranged on the water outlet pipeline; a bypass pipeline is arranged between the water inlet pipeline and the water outlet pipeline; and a second electromagnetic valve is arranged on the bypass pipeline. The control method provided by the invention comprises the following steps: opening the first electromagnetic valve body and closing the second electromagnetic valve body; acquiring the required temperature of the heat exchange terminal; when the requirement temperature is higher than the first temperature threshold, starting the electric auxiliary heating device, so that the target temperature can be acquired by the heat exchange terminal; and when the required temperature is lower than or equal to the first temperature threshold, selectively starting the electric auxiliary heating device. During the heat supply process of the heat pump system, the heat supplied by an air-conditioning unit and that supplied by the electric auxiliary heating device can be combined, thereby improving the total heat supplied by the heat pump system.