This research presents a flyback switching power supply design which is based on DSP The basic principles of switching power supply are illstruated, the switching-state space averaging method is applyied to establish its large-signal model, on the basis of the large-signal model and specifications, some basic selection principle of parameters of many basic components such as filter capacitors, power switches, high-frequency transformer, and snubber circuit are discussed in detail. It is essential to develop a cost-effective power supply product to meet the needs of client.in the hardware research, in order to ensure superior output performance and isolation requirements, the output voltage sampling circuit is developed by using high-precision linear optocoupler; To guarantee the system's salty and reliable operation, a temperature detection link is added to prevent the device over-temperature failure. As for the control strategy, in order to ensure the system's dynamic performance and robust performance, fuzzy PID control algorithm is presented, on the base of the small-signal model of fly back switching power supply, the fuzzy rules table is designed, the algorithm complexity is moderate because much calculation is finished by looking up table. In order to overcome the serious interference from the switching behavior in the system, this article introduces the EMI filter design, at the same time, anti-jamming design of the system have also been elaborated.The simulation and experimental results to testify the fuzzy PID[1] controller which is adopted in the flyback digital switching power supply greatly improves the system dynamic response, reducing the system output voltage ripple.