Abstract: The lithium batteries and ultra-capacitors are connected as auxiliary power supply to the PEMF（Proton Exchange Memorance Fuel Cell Strack） based power supply system to improve the dynamic performance of the system. The lithium batteries and ultra-capacitors feature high charge/discharge rate for compensating abrupt load change. The model of the hybrid power system is developed. A classic PI control is used to manage the power distribution in the system. Simulation of the system is carried out, which shows the improvement of the system response to abrupt load changes.