Middle-line soft seal butterfly valve is the preferred conventional butterfly valve for pipeline. The utility model has the advantages of simple structure, small flow resistance coefficient, near-straight flow characteristics, and is free of debris, in light weight, convenient to be installed, and small in driving torque. This valve can be used to cut off media and also to regulate the flow of media used. Its actuating device can be made according to user's requirements, either in manual, electric, pneumatic, or other forms. Different materials are selected and seal rings of different materials are provided. The valve is applicable to different media and working conditions and makes the cost and performance to achieve the best match.The soft seal butterfly valve is suitable for the temperature lower than 120℃ and nominal pressure lower than 1.6 MPa,and it is suitable for the industries such as water supply and drainage, sewage, food, heating, gas, shipping, hydropower, metallurgy, energy system, and textile,particularly suitable for two-way seal box valve bodies that are easy to be rusted.