Abstract: In this paper, the demand response of active distribution network(ADN)are analyzed and summarized in depth. Load is classified according to its importance degree and its dependence on power supply. A power supply strategy in fault status is presented, which can actively control large power electric appliances to increase the power supply range and reduce fluctuation of DGs by applying electric water heater. To deal with the islanding complex problem based on load demand, a mathematical model for optimization issue is built, and the improved minimum spanning tree is used to solve the model. Simulation results show that the power supply range is larger than that by normal schedule, and the satisfaction of customers is greatly improved, which has certain guidance significance for islanding classification of ADN.