Provided is an air conditioning system using ground heat. The system includes one or more indoor units, at least one outdoor unit, a ground heat exchanger, and a plurality of auxiliary heat sources. The one or more indoor units condition indoor air. The at least one outdoor unit communicates with the indoor units via a plurality of pipes, and includes an outdoor heat exchanger where heat exchange occurs. The ground heat exchanger is connected with the outdoor heat exchanger of the outdoor unit, and laid under the ground to allow heat to be exchanged between ground heat and a circulating medium circulating through the ground heat exchanger. The plurality of auxiliary heat sources are installed on one side of the outdoor unit to assist heat exchange of the outdoor heat exchanger. Two or more auxiliary heat sources are simultaneously used, or one of them is selectively used.