Abstract: Evaluating the content of casting slab inclusion mainly depends on the area(volume)percent ofinclusion at present.According to the standards in the world, two indices for evaluating casting slab inclusion wereestablished, i.e.index of purity and rating number.The application showed that the two indices reflect the contentof casting slab inclusion and the inclusion influence on the quality of steel, such as the percent of pass of 304stainless steel grinding plate.