Abstract:The dissolving status of limestone and lime in the initial BOF slag was studied in the laboratory. The results showed that the lime block reacted with the partial initial BOF slag at 1550℃, however the produced phase was still solid and no liquid phase was formed. The limestone block was completely soluble in the initial BOF slag and the homogeneous liquid slag was formed. In the industrial tests the limestone was added into converter at the earlier stage and middle- late period. The melting status and dephosphorization effect were investigated. The result showed that when adding limestone at the earlier stage, the basicity of the formed slag was lower, about 1.5 at the earlier stage and reached expected indexes at the smelting end- point. The dephosphorization effects at the earlier stage were unsatisfactory and improved at the middle and late period. When adding limestone at the middle and late period, the slag basicity kept higher value during blowing process, which can be beneficial to obtain stable dephosphorization rate.