Abstract: A private electric vehicle quantity forecasting model is established from macro, medium and micro perspective based on system dynamics model. Then the charging and discharging characteristics of electric vehicles are analyzed. Besides, the Monte Carlo method is used to simulate the charging and discharging behavior of private electric cars. Finally, the actual data is used to predict the change of grid load curve considering large-scale electric vehicles accessing to the grid in the future. The results show that, in the case of unregulated charging mode, the larger the quantity of electric private cars is, the greater the difference between the peak and the valley load and the adverse impact are. Moreover, it is found by further calculation that private electric cars participating in the discharge can, to some extent, cut down the grid peak load increased by EV charging and has a certain peak-load shifting benefits.