Abstract: LF refining slag has an important role in LF refining process. Through the analysis of melting point，component activity，viscosity and sulfur distribution ratio, the refining slag of adsorbing inclusion ability and high desulphurization capacity had been designed. The main compositions of the refining slag were w(CaO)=55 %—59 %，w(Al2O3)=27 %—32 %，w(SiO2)=5 %—10 %，w(MgO)≤8 %，w(FeO+MnO)＜1 %. By material balance calculation, the slagging process had been devised and had been tested. The result showed that the composition of the slag can reach the target, and cleanliness of the product was obviously improved. The inclusion level of the product was all less than 1.0 grade, and the total oxygen mass fraction was between 0.0006 % and 0.0011 %，which was less than that of the old slag.

Key words: refining slag, component activity, viscosity, inclusion, sulfur distribution ratio