Based on the mass and energy conservation, the coupling dynamic model for interfacial reaction between slag and metal was established using metallurgical thermodynamics, dynamics and reaction engineering. The different influencing factors were investigated and discussed. The results of the model show that the mass transfer of Cr2O3 in the slag phase is suggested to be rate-determining and the coke as reducing agent should be supplemented in the slag continuously. The model described and resolved the process of chromium ore smelting reduction in a converter preferably. A reference and basis on the constitution of rational processing route for a practical stainless steelmaking were provided.