Rotating magnetic field is applied in up-leg of RH vessel to promote the removal of non- metallic inclusions of molten steel and to prolong the life of RH equipment. Physical and mathematical models have been developed to understand the two-phase turbulent flow considering the effect of the rotating magnetic field in the RH vacuum degassing vessel. Water model experiments verified that the gas bubbles can be moved toward the central zone of up-leg of RH vessel as the result of density difference between gas bubbles and liquid in the swirling flow. The larger circulation flow rate can be obtained in RH degassing vessel with the effect of swirling flow. A penetrating velocity, which does not change the equation characteristics but changes solution distribution, is proposed to revise the gas volume fraction conservation equation. A revised gas volume fraction conservation equation is successfully used to solve the gas distribution in RH vessel. If there is no swirling flow, the larger upward velocities and maximum of the gas volume fraction appear near wall of up-leg. If the rotating magnetic field is applied in up-leg, the larger upward velocities occur in the central zone of up-leg. These phenomena agree with the experimental observation. When the rotating electromagnetic force is applied, the numerical results showed that a swirling flow may be produced and extended into the vacuum chamber. As the occurrence of swirling flow in upper part of up-leg, the maximum of gas volume fraction moves toward the center zone of up-leg and the upward parabolic velocity distribution is also formed.