The utility model relates to an upper-mounted self-sealing ball valve which comprises a valve body, a valve seat, a ball, a valve rod and a valve cover. Sealing faces of the ball and the valve seat are in hard sealing fit, and the valve seat is of a floating type structure; the upper-mounted self-sealing ball valve is characterized in that a pushing-open device is arranged between the ball and the valve seat and composed of a pushing ring, a pin roller, a locating shaft and a moving ring; the valve seat is pushed by the pushing-open device to be open in the rotating process of the ball to enable the valve seat to be out of contact with the ball, non-contact opening and closing of the sealing faces of the ball and the valve seat are achieved, and the upper-mounted self-sealing ball valve has the advantages of being reliable in sealing performance, long in service life and the like. The upper-mounted self-sealing ball valve is used for high-temperature and high-pressure valves of boiler feed water systems of petroleum, natural gas and thermal generator sets.