With a large number of electric vehicles plugged into the interconnected power grid, their mobile charging mode will bring a certain impact on the power grid. Conversely, as a mobile energy storage unit, electric vehicles can participate in the frequency regulation of the interconnected power grid, but the current research concentrated on centralized V2G control or decentralized V2G control. Based on the dynamic model of electric vehicle energy storage battery, the load frequency control model of multi-area interconnected power grid with electric vehicle clusters was constructed. Based on wide area monitoring system and model predictive control method, the wide area decentralized load frequency predictive control of multi-area power grid was realized. The model of three-area interconnected power grid is built in Matlab/Simulink and simulation analysis is carried out. The results show that the frequency fluctuation of the interconnected power grid can be suppressed in a short time when the electric vehicle is used as a mobile energy storage unit, and the wide area decentralized predictive control method proposed in this paper can limit the frequency deviation of the three-area power grid to a smaller range and recover to steady state value quicker than the classical PI control method.