Mold powder entrapment is one of the affecting factors on faint-sliver defect in IF cold-rolled steel sheet in casting process. Based on the analysis of the defect, the composition of mold powder is adjusted. Otherwise, surface tension and viscosity of mold powder are raised. After taking these measures, mold powder entrapment and casting subcutaneous slag is decreased obviously. In addition, the rate of faint-sliver defect in cold-rolled IF steel sheet has been reduced from 5.21% to below 1.0%.