Base on the study of the light reflectivity of steel surfaces, the interaction of CCD Camera and Illumination is investigated through experience. A new bright-dark filed defect recognition method which combines bright-filed mode and dark-filed mode is proposed. The bright-filed defect and dark-field defect on the surface of the strip steel can be detected at the same time through this new way, and the quantity of the defect information is increased. Therefore, the recognized defect type is twice the tradition way. A new algorithm of defect detection which is proper to bright-dark filed mode is proposed, too. This method is based on the image fusion. Experiment results show that detection rate of defects is more than 95% while classification rate of defects is over 85%.