In order to improve the energy utilization efficiency and driving range of electric vehicle, an electromechanical flywheel hybrid system based on planetary gear power split is proposed in this study. First, based on the working principle of planetary gear, the performance of the system under six topologies was analyzed. The optimal design schemehe was confirmed. Specially, the speed regulating motor and the flywheel connect with sun gear and ring gear respectively, the power output from carrier. Then, to meet the design requirement of the vehicle, the parameters of electromechanical flywheel hybrid device, the drive motor and the transmission were optimized. Finally, a vehicle dynamic simulation model was constructed to analyze the dynamic and economic performances of the vehicle under different conditions. Results show that, compared with the original vehicle driven by a single motor, the new hybrid system designed is able to improve the vehicle economy effectively while maintaining the power performance. Under J1015, NEDC and HWFET cycles, the average operating efficiencies of the power system are increased by 8.2%, 5.6% and 4.3%. [ABSTRACT FROM AUTHOR]