The recycling of LF hot steel slag of casting residue from ladles can reduce the release of waste slag and the harm to the environment. The paper analyzed the desulphurizing ability and recuperability of LF hot steel slag. It can de-crease the consumption of slag charge critically after LF hot steel slag were recycled to the BOF or LF and took part in the metallurgic reaction. It can reduce the consumption of lime 5 kg/t after recycling LF hot steel slag 1-1.5 t per ladle. And it can cut the consumption of slag charge 10-15 kg/t after recycle casting residue 3-5 t per ladle. After adopting the slagging regime of adding lime powder to hot steel slag in LF,the end-point sulphur content was almost the same with the normal treatment with the same time since the slagging rate was improved,meanwhile the process saved the power consumption, but the effect on the pick-up of silicon and magnesium in molten steel should be considered. The hot recycling of casting residue lows the temperature of molten iron into the converter for steel-making,thus the low lance level during the whole BOF treating process was preferable. Under the condition of not influencing the production,the best utilizing method of hot slag lies in the application of LF hot steel slag into the converter.