A transient three-dimensional mathematical model has been developed to analyze the three-phase flow in a 150 t EAF(electric arc furnace)using oxygen.VOF(multiphase volume of fluid)method is used to simulate the behaviors of molten steel and slag.Numerical simulation was conducted to clarify the transient phenomena of oxygen impingement on molten bath.When oxygen jet impinges on the surface of molten bath,the slag layer is broken and the penetrated cavity in molten steel is created.Simultaneously,the wave is formed at the surface of uncovered steel on which the slag layer is pushed away by jet.The result of numerical simulations shows that the area and velocity of uncovered steel created by impingement,jet penetration depth change from 0.10 m2,0.0125 m/s,3.58 cm to 0.72 m2,0.1445 m/s,11.21 cm,when the flow rate of an oxygen lance varies from 500 to 2000 m3/h.The results have been validated against water model experiments.More specially,the relation between the penetration depth and oxygen flow rate predicted by numerical simulation has been found to agree well with that concluded by water model. A transient three-dimensional mathematical model has been to analyze the three-phase flow in a 150 t EAF (electric arc furnace) using oxygen. VOF (multiphase volume of fluid) method is used to simulate the behaviors of molten steel and slag. Numerical simulation was conducted to clarify the transient phenomena of oxygen impingement on molten bath. WhEN oxygen jet impinges on the surface of molten bath, the slag layer is broken and the penetrated cavity in molten steel is created. Simultaneously, the wave is formed at the surface of uncovered steel on which the slag layer is pushed away by jet. The result of numerical simulations shows that the area and velocity of uncovered steel created by impingement, jet penetration depth change from 0.10 m2, 0.0125 m / s, 3.58 cm to 0.72 m2, 0.1445 m / s, 11.21 cm, when the flow rate of an oxygen lance varies from 500 to 2000 m3 / h. The results have been validated against water model experiments. More specifically, the relation between the penetration depth and oxyg en flow rate predicted by numerical simulation has been found to agree well with that concluded by water model.