A mathematical model that can simulate the transient fluid flow phenomena in a continuous casting mold has been developed. In this mathematical model, multi-phase flow phenomena which consist of the Ar gas injected into the submerged entry nozzle, molten steel and solidified shell can be described. To verify theav ailability of the mathematical model, water cold model and fused metal hot model experiments were conducted and comparisons of the measured fluid flow phenomena were made with computational results. In the water cold model, the time fluctuation of the fluid flow just under the meniscus and the deformation of the meniscus shape were measured and in the fused metal hot model, effect of the Ar gas bubble on the fluid flow in the mold were investigated. Computational results gave good agreement with both experimental measured data. Real plant simulation were conducted to investigate the effect of Ar gas bubble on the fluid flow phenomena in the continuous casting mold by using this mathematical model.