The structure and working principle of hybrid energy storage system are introduced. The classical RC model of ultracapacitor is analyzed, and the topology of charging and discharging converter of energy storage system is studied. A ultracapacitor-battery hybrid energy storage system model based on bidirectional boost-buck circuit is constructed, and the charging and discharging process of the energy storage system is simulated by Simulink circuit according to the power tracking strategy. The simulation results show that the hybrid energy storage system has a better dynamic response than the single battery energy storage system, and it can quickly complete the power requirement of the system. The addition of the ultracapacitor can reduce the impact damage to the battery due to the sudden change of the load, and prolong the service life of the battery.