This paper introduces a single ended flyback switching power supply based on OB2273, and analyzes the design principle, function and working process of some modules. In order to meet the requirements of electromagnetic compatibility and stable output of power supply, the design uses EMI filter to filter out the interference, and uses the voltage regulator TL431 and optocoupler to realize the feedback. The experimental results show that the switching power supply has some advantages, such as stable output DC voltage, high conversion efficiency, small ripple, small size, with the expected effect attained.