Transient impact on fuel cell system due to stack current fluctuation sometimes causes severe degradation of some performances such as voltage variation, oxygen starvation, anode/cathode pressure disturbance, membrane dryout and voltage reversal. As these hazards are poorly understood at present, in addition to the complex dynamic response involving various time scales, few investigations are carried on to alleviate the stack current influence on fuel cell. This paper presents a power management system, by employing a DC-DC module, a battery, a controller and some other circuits, as well as a LQR algorithm, which, on the one hand, provides load with a approximately constant voltage, and on the other hand, stabilizes stack current by regulating charging or discharging current of the battery according to the change of load. Therefore, this system can achieve a function of insulation of fuel cell from its load in electrical sense, i.e. for the load, the power management system supplies sufficient current it need with a approximately constant voltage; for the fuel cell system, stack current is limited into an acceptable range. This power management system was verified on a testbench and shows good validity.