Abstract: A three-dimensional mathematical model for the simulation of molten steel flow based on the parameters of 300 t RH-MFB has been established, discussing the factors of influencing circulation flow rate.The gas-liquid two-phase flow has been treated and described by two-fluid model.The influences of process parameters under the same vacuum condition on steel flow field and circulation flow rate are simulated, such as argon blowing flux, depth of snorkel, nozzles arrange.The results show that keeping argon blowing flux no more than 4 000 NL/min, circulation flow rate would increase with argon blowing flow rate increasing and with the increase of depth of snorkel a certain extent;it was more proper to arrange nozzles in interleaving way than others.