As a kind of high power type energy storage device, super capacitor has been widely used in life. However, due to the low voltage of the capacitor, the super capacitor bank must be formed by seriesparallel connection in the actual energy storage system. Aiming at the problem of voltage unbalance in the series connection of supercapacitors, an improved capacitor voltage control circuit is proposed in this paper. The circuit consists of capacitors and switches and transformers, through the feedback control, simplified parameter calculation, improve the voltage uniformity. Finally, MATLAB/Simulink simulation results show that the voltage balance is fast, the error is small, and it is easy to expand under the control circuit. It has a high value in the application of capacitor energy storage system.