The utility model provides a hard-sealing and high-temperature ball valve which comprises a valve body, a disc spring, a front valve seat, a ball body, a valve rod, a back valve seat and a sealing ring. A liquid inlet and a liquid outlet are formed in the valve body, the ball body is positioned in an inner cavity between the liquid inlet and the liquid outlet of the valve body, the top end of the ball body is fixedly connected with the valve rod, the front valve seat and the back valve seat are arranged between the two side faces of the ball body and the valve body respectively, the front valve seat is a floating type valve seat, the disc spring is arranged between the front valve seat and the valve body, the sealing ring is arranged between the back valve seat and the valve body, and the back valve seat is directly screwed in the valve body through threads and compresses the sealing ring. According to the hard-sealing and high-temperature ball valve, due to the fact that the back valve seat is directly screwed in the valve body through the threads and compresses the flexible graphite sealing ring, sealing between the back valve seat and the valve body no longer depends on the fact that the disc spring compresses the flexible graphite sealing ring to guarantee sealing between the valve seat and the valve body. Accordingly, the sealing reliability of the ball valve is high, and the service life of the ball valve is long.