Purging plug with slits is widely used in the secondary refining process, and its service life determines the downtime and production efficiency. To achieve a good performance in service life, optimizing the geometric structure of the slit, which can alleviate the stress concentration around the slit, was employed using the finite plate model. Furthermore, the performance of the purging plugs with different shapes of slits in the refining effect was investigated by conducting the water model experiments. The numerical simulation results showed that the appropriate shapes of slits could alleviate the stress concentration phenomena. In the water model experiment, the mixing time of the purging plug with circular slits is lesser than that of the purging plug with rectangular slits when the gas flow is less than 6.02 L/min. Compared with the rectangular slits, the circular slits are detrimental to smaller and well-distributed bubbles. Thus, the inclusion removal rate of the purging plug with circular slits is approximately 10% larger than that of the purging plug with the rectangular slits.