In this chapter, kinetic considerations for the composition evolution of inclusions in the molten steel during the refining process were discussed. Kinetic models on the multi-phase reactions in literature were briefly reviewed first. Three kinetic models were summarized, including Coupled Reaction Model, Effective Equilibrium Reaction Zone Model, and Unreacted Core Model. A multi-phase multicomponent kinetic model considering reactions among steel-slag-slag modifier-inclusion-refractory-alloy-air during the ladle furnace refining process was established. The following reactions were detailed: the reaction between the inclusion and the molten steel, the reaction between the molten steel and the molten slag, the reaction between the molten steel and the lining refractory, the reaction between the molten slag and the lining refractory, and the reaction between the air and the molten steel.