A large number of unmanaged electric vehicles (EVs) connected to the power grid brings harm to the safety of the power system. By using the technology of V2G, EVs are connected to grid to participate in the system frequency modulation. However, the demand of batteries will be affected. In this research, by analyzing the distribution of probability density of EV battery state, the strategy of participating in system FM control considering battery state of charge was proposed. Based on the characterristics of battery of EVs, a model was built. The EV charging and discharging scenario, which aims at stability of the frequency fluctuation of the power grid, was simulated. According to the state of SOC of the battery, the simulation results based on the control strategy of Matlab/Simulink verify the actual effect of EV participating in the system frequency modulation.