Its structural feature is that while the double eccentric valve stem axis position is eccentric, the conical axis of the butterfly plate sealing surface is skewed to the cylinder axis of the body, that is, after the third eccentricity, the sealing section of the butterfly plate is not Furthermore, it is a true circle but an ellipse, and the shape of the sealing surface is therefore asymmetrical, with one side inclined to the center line of the body and the other side parallel to the center line of the body.