Abstract: A mathematical simulation of flow field in the vacuum chamber and ladle during RH degassing was carried out in combination with the RH refining equipment of a steel company. Based on the simulation results some phenomenon during degassing operation can be explained. Proved by the formula and data obtained from the practice the simulation result is reliable. Finally, the model was used to calculate the turbulent dissipation rate field and the relation of circulation flow rate in the RH device with the quantity of Ar blowing, and the optimum quantity of gas blowing for the RH refining process was suggested.