Ventilation butterfly valve is a kind of non-hermetic butterfly valve, which is used in the ventilation and environmental protection engineering of the chemical industry, building materials, power plants, glass and other industries. It is used as a pipe control device for gas medium to regulate or cut off the flow. This type of valve shall generally be installed horizontally in pipes. The new structure is designed and manufactured by welding the middle-line plate with the short structure steel plate. It is compact in structure, light in weight, easy to install, small in flow resistance and large in flow, avoiding the influence of high temperature expansion and easy to operate. No connecting rod, bolt, etc. inside, reliable operation, long service life. It can be installed in multi-station without the influence of medium flow direction.