According to the characteristics of the intelligent substation integrated monitoring system, such as multiple types of equipment, large amount of information and wide design fields, this paper studies the principle and structure of the intelligent substation auxiliary integrated monitoring system on the basis of the intelligent substation. The algorithm of moving object detection in video monitoring subsystem is studied deeply, combining with the advantages and disadvantages of existing detection methods, an improved frame difference method based on average background is proposed in this paper. The performance of the improved algorithm is analyzed by simulation. The results show that the performance of the improved algorithm is significantly improved, compared with the improved algorithm, the precision is increased by 30%, and the recall is increased by 41.33%, which has a certain promoting effect on the linkage of the auxiliary monitoring system. This study provides reference for the development of the intelligent substation auxiliary integrated monitoring system in China.