The invention discloses a bimetal hard seal fixed ball valve disassembly and assembly method and a special tool, and belongs to the technical field of nuclear-grade valve maintenance of nuclear powerplants. The disassembly method comprises the following steps: (S10) a valve ball is closed; and a nylon clamping piece is mounted in a valve ball runner; (S20) the valve ball is rotated; and the nylonclamping piece is wedged between a valve base and the valve ball to insert a valve base pin in a valve base ring groove; (S30) the valve ball is rotated to a closing position; and a nylon clamping piece is taken out; (S40) the valve ball is rotated to an opening position; and the valve ball is taken out; (S50) a sealing surface of the valve base and foreign matters in a valve body are cleaned; (S60) a valve base ejection block is mounted on the sealing surface of the valve base; and a top support rod connected with the valve base ejection block is provided; (S70) the top support rod is rotated to eject a valve base spring to take out the valve base pin; and (S80) the top support rod is reversely rotated to release the valve base spring to take out the valve base ejection block, the top support rod and the valve base module. The method finishes disassembly and assembly in less space in the valve body without damaging the valve base and the sealing surface of the valve ball, remaining dirt and influencing sealing.