Abstract: By analyzing the composition of liquid steel and the composition and petrographical characteristics of slag,the variation of slag composition during oxygen blowing,and the slagging processes and dephosphorization with the two slagging methods(scheme A and B) applied to the 210 t combined blowing BOF were investigated.A comparison between test results of the two slagging methods showed that scheme B was better than scheme A: first,the slag melted more rapidly at early smelting stage and the dephosphorization rate at early and medium smelting stages was 12.6% higher;second,the slag fluidity was better and mineral phase with high melting point was found less;third,the slag composition fluctuated more smoothly;fourth,the consumption of lime decreased by 11.5 kg/t,the L_p increased by 5.42,and the average dephosphorization rate of BOF increased by 2.7%.