Abstract: A mathematical model was established and applied to simulatethe decarburization of RH-MFB process in Pansteel Company. Study of the effects of w_c, w_o, Ar flowrate, evacuation rate and MFB lance blowing parameters on the decarburization process was carried out. The results showed that this model could give the quantitative understanding of the process, especially the behavior of MFB lance blowing. This model has realized the optimum process of RH-MFB refining for ultra-low carbonsteels in Pansteel.