Abstract: The characteristics and source of high SiO₂ inclusions in IF steel slab were studied through a variety of methods,such as X-ray diffraction(XRD),scanning electron microscopy/energy dispersive spectroscopy(SEM/EDS),and non-destructive inclusion extraction. Results showed that many solid macro-inclusions existed in the IF steel slab,and the high SiO₂ inclusions in irregular shape and large size(> 50 μm) occupied 60% of the total number. This kind of inclusions was mainly from the bad pre-melt mould power.High-melting-point solid oxides,such as SiO₂ and Al₂O₃ existed inside the power particles,and these solid oxides were captured by the shell before dissolved completely during the casting,and finally formed inclusions in the slab. quality defects of the slab caused by high SiO₂ inclusions can be reduced by improving the pre-melting performance of the mould powder.