Abstract: This paper analyzes an alarm event of air leakage in the air chamber of the grounding knife on the main transformer side of a 220 kV switch. The composition of GIS equipment and the common causes and effects of SF₆ gas leakage are introduced. In the case of this article, a leakage fault occurred in the air chamber of the grounding knife brake of a 220 kV main transformer switch. After inspection, it was found that there was a crack in the insulating flange. In order to analyze the cause of the incident, the appearance and materials of the faulty components were analyzed, and research tests were conducted in groups, and a method to fundamentally prevent the corrosion and cracking of the insulating flange metal inserts was found.