The present invention relates to a sheet structure of a trunnion type ball valve which watertight structure is improved. The sheet structure of the trunnion type ball valve includes a valve body (1); a cap (3) fixed to both sides of the valve body (1); a valve stem (9) installed on the valve body (1) in a direction perpendicular to a conduit line (W); a ball (15) connected to the tip end of the valve stem (9); a sheet ring which is installed between the ball (15) and the cap (3) and which is in face-contact with the ball (15); and a sealing member for preventing a fluid leakage. The sealing member includes a pressure gasket (29) of a wedge form fitted into the boundary of the sheet ring (19) and the cap (3); and a ring-shaped leaf spring (35). One end of the leaf spring (35) is in contact with the sheet ring (19), and the other end thereof is in contact with the cap (3) so that the sheet ring (19) receives an elastic force toward the ball (15).
