Compared with the traditional butterfly valve, the flange triple offset butterfly valve has high temperature resistance, light operation, no friction to open and close. And the seal is compensated with the increase of the torque of the transmission mechanism when closing, which improves the sealing performance of the butterfly valve and prolongs the service life. The valve body and the valve seat are joint members, and the sealing surface of the seat is welded with a temperature-resistant and corrosion-resistant alloy material like stellite. A multi-layer soft stack seal is attached to the valve disc.