Abstract: During opening of a hot-rolling Q345B steel strip, severe surface defects which are mainly holes, folding and cracks, were found on one side of the whole strip. Formation reasons of these surface defects of the strip were analyzed by chemical compositions analysis, inclusions examination, fracture analysis and microstructure observation using SEM. The results show that the surface defects were possibly caused by the scaling of oxide on the working rollers. Scaling of the oxide made the surface of the working rollers became coarse, which resulted in the formation of the folding defect. Then folding developed into hole and the impressing of the oxide resulted in the formation of the crack.