Abstract: Based on the coexistence theory of steel slag structure and the programming theory, a mathematical model revealing the relationship between inclusions and molten steel composition in a continuous casting mold was developed with the aim to minimize the free energy change of the reaction between inclusions and liquid steel. It is verified by the experiment that results calculated with the model are agreement with the experimental ones well when the inclusions are in liquid state. The effects of[Ca] and[Al] contents in liquid steel oh the inclusion components were discussed and the results show that[Al] content should be changed with[Ca] content in liquid steel in order to acquire deformable inclusions in tire cord steel. When the mass fraction of[Ca] in liquid steel is 5 ×1010^-6, the mass fraction of[Al] should be controlled around 12 ×10^-6.