The invention discloses an uninterrupted power supply system and method with the mixture of a fuel cell and a super capacitor. The system comprises mains supply, a power conversion system, a backup power supply and a load. The fuel cell and the super capacitor are used as a backup power supply, when the mains supply is cut off, the small-capacity long-life supercapacitor can instantaneously supplypower to the load, a condition that the fuel cell directly drives the load to carry out cold start is avoided, the response time of the uninterrupted power supply system is reduced, and the safety and life of the fuel cell are improved. A mature average current mode, constant frequency control and voltage outer loop current inner loop double-closed-loop control are used by an active power factorcorrection circuit, the system has the advantages of a small volume, low power consumption, high efficiency, a high power factor, small total harmonic distortion an high safety and reliability, the uninterrupted power supply for a long time can be ensured, the control of a power tube of the invention is simple to realize, the numbers of diodes and power tubes are small, the cost is low, the efficiency is high, and the safety and reliability are high.