Abstract: This paper proposed a reactive power optimization model of high voltage distribution network considering the cycle control for direct load control（DLC） of air-conditioning loads.First,under the analysis of the cycle control characteristics of air-conditioning load,the critical starting voltage of multi air-conditioning governed by a load aggregator was derived,based on the steady-state equivalent of air-conditioning load and the Thevenin equivalent of distribution transformer network.Then,two layers of the load side and power side are considered for constructing this model,which included the optimal allocation model of DLC air conditioning load reduction and reactive power optimization model considering transformer tap-locking.Furthermore,these two models are combined.For the former one,the immune genetic algorithm is adopted to obtain the start-up voltage constraints of air conditioning which were introduced to the later model.Namely,the proposed model was established and was solved by interior point method.Finally,the effectiveness of the proposed model is verified by simulation analysis of an 110 k V distribution network with 25 buses and a 10 k V feeder system managed by a load aggregator in Chengdu.