The utility model relates to a slagging-off device of steel ladle. The slagging-off device of the steel ladle comprises a slag basin, the steel ladle arranged above the slag basin in a hung mode, and a slagging-off device, and further comprises a vertical plate arranged on one side of the steel ladle. An observation hole and a slagging-off hole enabling the slagging-off device to pass through are formed in the vertical plate. A guide roller component used for supporting the slagging-off device is further arranged on a position, facing towards the slag basin, of one side of the vertical plate and located on the lower side position of the slagging-off hole. The slagging-off device of the steel ladle can effectively prevent liquid steel from spurting the body of an operator and eliminates potential safety hazards. Meanwhile, the overall weight of the slagging-off device is borne by the guide roller component, so labor intensity of operating workers is effectively lightened.