U type butterfly valve adopts the top-mounted structure, which reduces the connecting bolts of the body itself under high pressure and large caliber conditions, enhances the reliability of the valve and overcomes the influence of the system self-weight on the normal operation of the valve. Simple structure, good interchangeability, easy to maintain and disassembly, stem seal is not easy to change, avoid stem leakage, seat sealing surface and backrest as one, reduce the deformation of the seat.