Sulphur has been reduced from 0.02wt% to 0.002wt% in 38 min average during 200 t ladle treatment in 2# steel plant of Capital Steel.The sulphide capacity and equilibrium sulphur distribution of slags are calculated and compared with the measured values.The results show that the KTH model is a useful tool for the prediction of sulphide capacity and sulphur distribution during ladle treatment; the desulphurization reactions are completed nearly in thermo-equilibrium.