Abstract: The mass transfer of benzoic acid between water and oil has been performed to simulate the mass transfer processes of metallurgical reactions in gas stirred ladles, and effects of gas flow rate, slag volume, tuyere positions on mass transfer rate have been studied when the rate controlling process is mass transfer in slag.The results show that mass transfer rate increases with the increasing of gas flow rate, and increases abruptly at a critical gas flow rate, for mass transfer of benzoic acid the dependence of kA on Q was kA∝Q^0.20 in low gas flow region and kA∝Q^0.80 in high region, the abrupt rate increase is due to increase of interface area begotten by entrapment of slag;mass transfer rate also increases with increasing of slag volume;centric gas bubbling could reach higher mass transfer rate than off-centric positions, so it is suggested that the determine of optimum tuyere position should based on both mixing time and mass transfer rate.