In order to analyze the CO 2 emissions reduction effect produced by the technology substituting limestone for lime to slag in BOF， some data of the energy consumption and CO 2 emissions were calculated by comparing the mode charging limestone directly into converter for slagging with the mode calcining limestone for lime then charging lime into converter for slagging. The results showed the CO 2 emissions of 1.29 and 1.12 kilogram can be reduced in the condition of 1 kilogram lime being replaced by limestone， using steel scrap and iron pig as cooling agent respec- tively. This technology will bring huge environmental benefits for the steel industry.