Both the fuel cell and battery have timely dynamic response to the step-profile load input. The current overshoot followed by a voltage undershoot behavior happen the step-up load, particularly. These phenomena are closely related to mass transfer mechanisms such as the water/gas transport by the redistribution of membrane water content in the fuel cell and the charge double-layer effect in the battery. When the load demand is beyond the rated power of the fuel cell system, the battery immediately powers to the load with a transient discharging current especially in the step-profile load power. This study presents a new control strategy for hybrid fuel cell-battery power sources with transient and overshoot considered. The results show that the proposed hybrid fuel cell-battery power source not only acting as a power stabilizer but also dynamically satisfying the step-profile load demand.