The quality of the CSP-hot galvanized sheets was decreased by some sliver-type surface defects. The morphology, structure and component of the defect were analyzed by using optical microscope, XRD and SEM-EDS. The results showed that the oxides(FeO)formed in CSP hot rolling led to the defect. The oxides were pressed in or elongated in the surface layer of the steel in a centimeter-scale to meter-scale during hot rolling and cold rolling. Finally the oxides were rolled into point-chain shaped lines along the rolling direction. Appearance of the lines were intensified by galvanizing. Accordingly, the measures of reducing oxides on the surface of steel in production were supposed to eliminate the defect.