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Na₂O is an alkaline oxide, which can significantly improve the dephosphorization ability of converter slag. The effect of Na₂O on the dephosphorization of converter slag was analyzed with a high-temperature dephosphorization experiment in a MoSi₂ resistance furnace. We found that the dephosphorization rate increased with the increase of (Na₂O) in the dephosphorization slag. The elements of Ca, Si, O, and P in the dephosphorization slag are distributed in the same area, mainly in the form of phosphate minerals, such as Ca₂SiO₄·0.05Ca₃(PO₄)₂ and 6Ca₂SiO₄·Ca₃(PO₄)₂. After adding Na₂O, part of the Na will replace the Ca in the phosphorus-containing phase to form Ca₂SiO₄·Ca₂Na₂(PO₄)₂. The industrial test showed that the average dephosphorization rate in the early stage of the test heats with the CaO-MgO-FeO-SiO₂-0.5%Na₂O slag system could reach 62.39%, which was 19.62% higher than that of the conventional heats. The average basicity of the final slag was 0.19% lower than that of the conventional heats, while <i>w</i>(P₂O₅) increased by 0.36%, and T.Fe decreased by 0.69%. The average consumption of the slagging materials was 35.93 kg/t, which was 7.24 kg/t less than that of the conventional heats. Through thermodynamic calculation, we found that with the increase of (Na₂O), the phosphorus distribution ratio between slag and steel increased significantly, the area of the liquid phase zone of the slag system increased continuously, and the viscosity decreased continuously.