Abstract: The advantages of electric vehicle make it receive wide attention and application. However, the spatial and temporal distribution uncertainties of the electric vehicles will adversely affect the electric power system operation. Then there exist security operation risk in distribution network operation. A dynamic distribution model for charging power of electric vehicle is built in this paper. And a dynamic probabilistic load flow method for distribution network with electric vehicles is also proposed based on semi invariant and Gram Charlier series. Furthermore, the off limit risk indexes of bus voltage and line flow are built, and an operation risk assessment method for distribution network with electric vehicles is proposed. The simulation results of IEEE 33 bus system show that the operation risk assessment of distribution system with electric vehicles are feasible, and the weak point of the distribution network in different time periods can be scanned.