The invention discloses a method of synchronously processing liquid blast furnace slag, chromic slag and sludge. Blast furnace slag is heated, and sludge is gasified; then catalysts such as hazardous waste chromic slag and the like are used for catalyzing and splitting sludge at a high temperature; on the condition of steam gasification, the sludge is converted to low-molecular high-temperature energy gas thoroughly, so that coking on the surface of the chromic slag is avoided; at the same time, high-temperature energy gas is used for heating chromic slag, and hexavalent chromium in the chromic slag is reduced to trivalent chromium; and the energy gas is cooled incidentally, and CO2 and C1 in the energy gas are absorbed by alkaline substances in the chromic slag. According to the technology, the chromic slag is reutilized and the blast furnace slag is cooled, so that energy is greatly saved; and at the same time, high-grade energy gas is obtained.