Abstract: This paper analyzes an event of abnormal opening of a 220 kV substation bus switch. After the first and second equipment inspection and analysis of the abnormal opening event, the cause of the abnormal opening event of the switch was determined, and the whole process of the abnormal opening event was analyzed. It was discovered that during work, the staff found that the data of the temperature and humidity sensor in the three-phase inconsistent terminal box of the line switch was abnormal, and then the temperature and humidity sensor battery was replaced at the threephase inconsistent terminal box of the switch body, which caused the switch to be abnormally opened during work. The incident exposed the poor safety awareness of the analysis staff, insufficient identification of dangerous points, and irregular construction that caused the K38 (K37) relay to operate, causing the switch to open abnormally. The problems exposed by the incident also remind us that all aspects of equipment management and operation should be rigorous and meticulous to avoid such incidents from happening again.