Abstract: To understand the characteristic of mixing in 210 t RH vacuum refining process,a 1:4 water model was established to investigate the effects of gas flow rate,snorkel immersion depth(SID),vacuum chamber pressure and number of blockage blowing air holeon the RH mixing time. The results show that the RH mixing time presents a decreasing trend with the increase of gas blowing andthe decrease of the vacuum chamber pressure. Furthermore,the mixing time first decreases then increases with the increaseof the snorkel immersion depth(SID) and the number of blockage blowing air hole,and the optimum SID is 480 mm. Using particle imagevelocimetry to measure the two-dimensional flow field of RH ladle in refining process,and then compared to the results of numerical simulation,the results show that the fluid movement in the ladle is mainly the circulation flow from down-leg to up-leg andthe back-flow around the down-leg. In addition,the inactive region is mainly located in the range of SID under the steel-slag interface.