Abstract: The intelligent recorder is a kind of new recorder that can be applied to both smart substations and conventional substations. It integrates the functions of fault recording analysis, network record analysis, secondary system online monitoring, intelligent operation and maintenance, etc. Among them, the online monitoring of the secondary system is one of the important technical updates of the traditional recorder. This article takes the 500 kV Danxia substation in Shaoguan, Guangdong as an example to analyse several application examples of secondary system online monitoring technology based on intelligent recorder, and study its role in the daily operation and maintenance, abnormal analysis and hidden danger elimination of the secondary system of 500 kV intelligent substation, and suggest improvement ideas for deficiencies, discuss its application prospects in improving the level of intelligent operation and maintenance and the direction of maintenance efficiency.