The detection and classification of real-time surface defects play an important role in automotive sheet inspection and production. In this paper,an automatic surface inspection system( ASIS) based on signal processing in Baosteel NO. 4 cold-rolled plant is briefly presented. We demonstrate that the strip surface defect properties such as image,type,pitch,and position can be accurately calculated and classified by the automatic surface inspection system.In the manufacturing of the high-quality cold-rolled strips,it is necessary that the real-time surface defects can be detected and transferred by the automatic surface inspection system combined with annealing lines and recoiling lines. The detection and classification of real-time surface defects play an important role in automotive sheet inspection and production. In this paper, an automatic surface inspection system (ASIS) based on signal processing in Baosteel NO. 4 cold-rolled plant is briefly presented. We demonstrate that the strip surface defect properties such as image, type, pitch, and position can be precisely calculated and classified by the automatic surface inspection system.In the manufacturing of the high-quality cold-rolled strips, it is necessary that the real -time surface defects can be detected and transferred by the automatic surface inspection system combined with annealing lines and recoiling lines.