In order to meet the demand of each monitoring unit module in wind power generation system, a multi-output DC auxiliary switching power supply is designed. According to the specific requirements of relevant parameters of auxiliary power supply, the DC-DC high-frequency flyback transformer was theoretically analyzed and designed; The voltage regulator TL431, optoelectronic coupler PC817 and UC2842 control chip were selected to realize the collection of output voltage, input current and drive of power MOS tube; A flyback switching power supply circuit with multiple output and double closed-loop control with output voltage of 5 V, 15 V and 24 V was built, and the circuit simulation of the designed DC auxiliary switching power supply was carried out by using Saber software. The simulation results show that the output voltage,duty cycle and switching frequency of the designed multi-output DC auxiliary switching power supply meet the design requirements, and their values are all within 10% of the design accuracy requirements. It is concluded that the method adopted in the design of auxiliary power circuit in this paper is simple and effective, and the selection of the parameter valuesSof each component of the circuit is reasonable, which can provide a reference for the optimization of parameters of each component in the subsequent hardware development of the circuit of the DC auxiliary power system.