Abstract: The monitoring terminal power module of substation auxiliary equipment provides hardware support for collecting the status data of auxiliary equipment and controlling the working status of auxiliary equipment. Therefore, a design method of monitoring terminal power module based on single live wire and neutral-live wire is proposed. Firstly, the working principle of single live wire and neutral-live wire is analyzed, and then the corresponding power taking loop is designed. Secondly, the capacity range of the access load is determined and some improvement measures to increase the capacity range of the access load are put forward according to the calculation formula. Finally, the simulation circuit and test platform are built, and the output voltage and the voltage and current waveform of key components are measured respectively under the single live wire connection mode and neutral-live wire connection mode, which verified the reliability of the power module under the two connection modes and the correctness of the access load capacity range. The experimental results show that the performance of the improved monitoring terminal power module is stable, and its access load capacity range has been effectively improved.