The purpose of this study is to develop a computer simulation system to analyze the multi-phase (gas-liquid-slag) flow phenomena in the direct iron ore smelting reduction process to evaluate the conditions of stirring and mixing induced by gas-jetting. A computational fluid dynamics technique; called the SOLA-VOF method, has been used to treat flow behavior of molten iron with free surface. As to the issue of the multi-phase, the Langrange and Quasi-Single Phase concept were applied to analyze the flow behavior of the injected gas, molten iron, and slag. The simulation system can be directly applied to analyze stirring processes at high flow rate gas and its related turbulent free surface. The developed system was then applied to analyze the flow behavior in the 60 % reduced smelting furnace. Interactions between inserted gas and liquid bath, agitation of slag and mixing conditions of liquid bath and slag under different gas flow rates, bubble sizes, and arrangements of bottom-blown tuyeres were evaluated in this study. The simulation results were then compared with water model experiments under similar flow conditions and were found to closely correspond with the experimental results.