Abstract: To grasp the mass transfer in RH-KTB vacuum refining process, a water modeling was done on the scale of 1:5.5, and the NaOH-CO2 solution system was used to investigate the effects of different process parameters on the oxygen absorption, decarburization and degassing processes. The experimental results showed that either increasing the lifting gas flowrate and top blowing gas flowrate or decreasing the top lance height benefit the absorption rate of top blowing oxygen, while increasing the lifting gas flowrate benefits decarburization. The liquid surface level in the vacuum chamber has an optimum value for the absorption process of oxygen. When blowing oxygen with a top lance, the vacuum degree should reach its optimum value for fast absorption of oxygen. Moreover, when stopping the top blowing oxygen operation, the vacuum degree should be increased as high as possible to accelerate decarburization.