Abstract: The energy storage property of the air conditioning system are studied firstly, based on which, the energy storage model for air-conditioning system is put forward. Then, the air conditioning load aggregation model and the charging /discharging control model of energy storage element in secondary frequency regulation of power system are mainly studied. In load aggregation model, the cluster load of air conditioning will be integrated into a virtual AGC generator unit, with the representation of its regulation capacity, regulation speed and regulation precision. The AGC instructions will be inversed into open or stop control signal of air-conditioning equipment through the charging/discharging control model. Finally, the characteristic of virtual AGC unit is analyzed, and the effectiveness of the air conditioning participating in secondary frequency regulation is verified in the case study.