Abstract: To solve the problems of short cycle life and small power density of single battery energy storage system in hybrid electric vehicles (HEV), a battery-ultracapacitor hybrid energy source was proposed. Then, the model of battery pack and ultracapacitor in parallel connection was established based on AVL-Cruise/Simulink, and a hybrid energy storage system control strategy was joined in energy management strategy of the best engine running condition. The hybrid energy storage control strategy was designed to relax the shocking of large current to the battery when starting and braking engine, to make the battery work in a high efficient range so as to improve the vehicle fuel economy. On this basis, battery and ultracapacitor parameters were matched. And the simulation results show that large current charge-discharge of battery pack can be reduced obviously, and the fuel economy of HEV can be improved as well.