The invention relates to a flow-split disk used for disposing the hot-state furnace slag and a method for joining the flow-split disk used for disposing the hot-state furnace slag. The flow-split disk consists of a frustum member and a cone-shaped support which are joined together by adopting internal assembly method. The frustum member consists of a plurality of segments shaped like the Chinese character 'ge'. Each segment consists of three fan-shaped ring plates which are arranged to form the shape of the Chinese character 'ge' and fixedly and mutually connected with rib plates. Connecting plates with threaded holes are arranged on two end surfaces of each segment. The segments are connected as a whole via bolts. The cone-shaped support has a frame structure shaped like the Chinese character 'sa' and is formed by fixedly connecting an intermediate ring plate, lateral ring plates on two sides, a shaft sleeve perpendicular to the support and a rib plate, wherein the diameter of the intermediate ring plate is slightly larger than that of the lateral ring plate. The intermediate ring plate of the cone-shaped support and the middle plates of the segments of the frustum member are fixedly connected via bolts, so as to form the flow-split disk. A lateral panel is covered on the lateral ring plates. The flow-split disk prolongs the service life and improves the safety of the flow-split disk.