Abstract: Outdoor cabinet in substation is an important equipment in the station. In recent years, dc grounding, false alarms, electric operation of equipment and other defects frequently occur in substations, and most of them are caused by dampness of equipment mechanism box and terminal box, corrosion and damage of components and terminals in the box. The rain proof performance of mechanism box itself is the key to determine the stable and reliable operation of equipment. In view of the above phenomenon of water intake and dampness of the mechanism box, the waterproof jacket is designed and manufactured for the surface of the vertical connecting rod and the mechanism box of the open isolation switch. It solves the problems of slow infiltration and backflow of rain water in the surface seal of the mechanism box between vertical connecting rod and rotating shaft of the open isolation switch, and effectively guarantees the safe operation of the equipment.