Active management of grid-connected distributed generators（DG）and energy storage system（ESS）can be used to suppress the load fluctuation of active distribution network（ADN）and the intermittency of renewable energy.A power supply and storage capacity（PSSC）index of local autonomy area is proposed to quantitatively measure the capacity of energy storage to supply electric power.The local autonomy area with DG/ESS and loads is analyzed as a whole considering network restrictions and specification constraints of DG/ESS.PSSC index of an ADN feeder is also proposed to quantify the maximum power exchanged between ADN feeders.The algorithm of PSSC and the operation optimization model of ADN based on PSSC is then put forward.The security constraints of power supply in the distribution network is also considered in this model.The efficiency of the PSSC index of local autonomy areas and feeders as well as the improvement of operation efficient is analyzed through case studies.