A quantitative evaluation method for the magnesia refractory deterioration in the smelting process is proposed based on analysis of static and rotating finger tests to study the dissolution behavior. A transient 3D fluid-solid coupled numerical model was then developed, including the two-phase gas/slag flow pattern, temperature profile, MgO content distribution, solid refractory dissolution, and sample shape change. A kinetic degradation model was introduced to calculate the refractory overall wear rate determined by the coupled effect of the flow-induced erosion and chemical-induced corrosion. The shape change of the solid refractory sample was characterized via the dynamic mesh technique. A close correlation between the simulated results and the experimental data gives confidence in the fundamental validity of the developed numerical model. The results indicate that the flow would increase the overall wear rate by one or two orders of magnitude depending on the velocity. Therefore, flow-induced erosion must be accounted for in estimating the refractory wear rate. The flow-induced erosion and chemical-induced corrosion could be quantified via the wall shear stress and a modified Arrhenius’s law, respectively.