A model for the action concentrations calculation of structural units in Na2O-TiO2-SiO2-CaO-Al2O3-V2O5-MnO-MgO-FeO slags and a thermodynamic model of the sulfur distribution ratio between slag and hot metal have been developed based on the ion-molecule coexistence theory (IMCT), and the model was verified by sodium oxide smelting experiments. The theoretical calculation results showed the composition of the main structural units and the activities of Na2O, CaO, MnO, MgO, and FeO in slag at 1200℃. The formation of compounds with a low melting point can be promoted by the addition of Na2O, meanwhile, the content of substances with high melting points decreases, which led to a decrease in the melting temperature of slag and the improvement of dynamic conditions of desulfurization reaction. Besides, the activities of Na2O and CaO increased with the increase of Na2O, thereby the activity of S2? decreased, and the desulfurization reaction between slag and hot metal can also be enhanced. The experimental results revealed that the sulfur distribution ratio between slag and hot metal improved by the increase in RN/C, which was beneficial to the deep desulfurization process of hot metal, and the sulfur can be removed to less than 0.0005wt%. The theoretical calculation results of the sulfur distribution ratio were in good agreement with the experimental results, which indicated that the sulfur distribution ratio can be well predicted by the model during the sodium oxide smelting process. The sulfur distribution ratios of basic oxide in the slag increased with the RN/C increasing and were ranked as Na2O>CaO>MnO>FeO>MgO. The IMCT was successfully applied to the investigation of the mechanism for the desulfurization reaction process between slag and hot metal in the Na2O-TiO2-SiO2-CaO-Al2O3-V2O5-MnO-MgO-FeO slags, which provided a theoretical basis for the optimization of slags in the deep desulfurization process of hot metal.