Slot plug is one of the most important units for bottom powder injection, and the parameters of slits on slot plug significantly influenced the direct motion of technique. In this paper, the parameters of slits such as thickness, width and length were theoretical studied and proposed a projected dimension. It was indicated that the optimal parameters of slits on slot plug using in bottom powder injection desulfurization was listed as follows, length exceeded 160~250mm, width exceeded 10mm, thickness was 0.15mm, and the slits should circular symmetric distribute on slot plug. The slot plug with parameters described above was industrial desulphurization tested in a 20t foundry ladle and feasible. Besides, the foundry ladle with the design and application of slits on slot plug used for bottom powder injection desulfurization was safety in production.