Circular slits are introduced in purging plugs for alleviating the stress concentration to prolong their service life. Herein, the effects of slits with different geometries on the mixing time, inclusion removal rate, and slag eye area are studied by water model method. Experimental results show that the inclusion removal rate decreases with increasing slit angle for the gas flow rate of less than 6.02 NL min ⁻¹. Moreover, with slit diameter increases, the mixing time and inclusion removal rate decrease when a gas flow rate is less than 5.26 NL min ⁻¹. The slag eye area increases with increasing slit diameter, and the slit angle has a positive influence on the formation of the slag eye. Finally, the optimization of the mixing time and inclusion removal rate for less consumption of stirring energy and less slag entrapment indicates that the smaller the slag eye area is, the better the refining effect is.