Abstract: The engineering method of energy storage sizing and the operation and management of electric vehicles（EVs） were studied considering the moving load and storage characteristics of EVs in microgrids. The value at risk（Va R） theory was applied to evaluating the risk of the configured storage. Three EV regional energy management modes including uncoordinated charging, coordinated charging and coordinated charging/discharging were formulated utilizing a price incentive model. The optimal storage size was calculated by minimizing the comprehensive cost of microgrid in a day in grid-connected mode. The impacts of interactive power penalty coefficient and fluctuation on selecting storage size were also analyzed. Va R theory was applied to analyzing the islanded operation risk in various energy managements and the feasibility of the configured storage size was verified. The simulation result validates that compared with uncoordinated charging mode, coordinated charging and coordinated charging /discharging modes reduces storage size, lowers the comprehensive cost and decreased the fluctuation of interactive power. Compared with no EV participating in islanded microgrid, the length of islanded time is extended and the risk of autonomous islanded operation is decreased significantly when encouraging EV to discharge.