The invention discloses a method for separating cast sludge from the molten steel, comprising following steps: pouring both the cast sludge and the molten steel in the ladle into an exclusive sludge ladle; delaminating the sludge and the molten steel by using the exclusive sludge ladle; discharging molten steel by using an exclusive sludge ladle; pouring residue cast sludge in the sludge ladle; recovering and treating the cast sludge and the molten steel respectively. Or the invented method comprises following steps: pouring both the cast sludge and the molten steel in the ladle into an exclusive sludge ladle; delaminating the sludge and the molten steel by using the exclusive sludge ladle; pushing out cast sludge by using a drossing machine; pouring residue molten steel in the sludge ladle; recovering and treating the cast sludge and the molten steel respectively. By using the invented method, the cast sludge and the model steel are separated simply and cleanly without pollution, energy waste is avoided by using self heat quantity of the molten steel, and cooling and blocking of the cast sludge and the model steel can be avoided at the same time. In addition, the cast sludge and the model steel can be separated quickly and recovered respectively, so that the productivity and economic effectiveness are increased.