Abstract: Outdoor H.V. switchgear is an important part of power transmission and distribution, which is distributed in urban and rural areas. In case of fire, it will not only cause serious economic losses, but also cause casualties. This paper summarizes some causes of fire in H.V. switchgear, proposes to develop a small outdoor ring main cabinet fire extinguishing device, which can replace the power operation and maintenance personnel to extinguish the fire at the first time, and verifies the fire extinguishing effect.