Abstract: The stain defects on cold-rolled steel sheet affecting the quality of coating product seriously were analyzed by methods of auger electron spectroscopy, glow discharge spectrometry, electro-chemical analysis, metallographic examination and so on.The results showed that the stain defects occurred on the external surface of inner ring and the adjacent inner surface of outer ring of steel plate, caused by the residual water vapor on the plate surface after degreasing process.After annealing reduction and rolling by flat roller, the visible strip defects formed along rolling direction.