The invention discloses a soft sealed butterfly valve composed of valve body, butterfly board, valve rod, end cover, valve seat, bearing, sealing piece and driving device, where the butterfly board is a tri-eccentric structure, and its main character: the valve seat is a metal outer lined plastic structure formed by coiling and sintering metallic frame on plastic thin film. It has the advantages of small cold-flow deformation, good sealing performance, small operating torque, long service life, wide application range, especially applied to make large-bore butterfly valve.