The hybrid energy storage system（HESS）uses Battery-Supercapacitor to suppress the DC bus current fluctuation caused by the load fluctuation. The traditional HESS uses a boost circuit to connect the HESS and the DC bus. However, the Boost circuit has the disadvantages of large output current ripple and interrupted output current. Using the H-bridge DC-DC converter connects the DC bus and the HESS, which can reduce the output current ripple and can stabilise the output current when the load suddenly changes. The proportional gain KP and the integral speed KI of the PI controller will restrict the flexible adjustment when the load is suddenly changed. The improved self-adaptive fuzzy PI controller is used to control the charging and discharging of the battery. The intelligence of the fuzzy control（FC）can be used in combination with the PI control to restrict the current fluctuation caused by the pulse load in quantitative adjustment. To verify the proposed method, a MATLAB/Simulink model was set up. Then the pulse loads were set to be added in 4.0s-7.0s and 10.0s-11.0s.The simulation results show that the system uses the Boost controller and the improved self-adaptive fuzzy PI control strategy can stabilise the output current in 0.3S; Using the H-bridge DC-DC converter and PI control strategy can stabilise the output current in 0.2S; Using the H-Bridge DC-DC converter and the improved self-adaptive PI control strategy can stabilise the output current in the moment of load fluctuation. Therefore, using the H-bridge DC-DC converter and the improved self-adaptive fuzzy PI control strategy can be the best one to stabilise the current fluctuations when the load changes.