Abstract: The surface of a produced horseshoe black spots and other surface defects. Through the study of the corresponding relationship between the hot rolled sheet and the same batch billet, the generation and evolution behavior of defects were analyzed, and the evolution process and law of the defects were further traced back. The results show that the defects of horseshoe black spot in hot rolled sheet are mainly caused by rolling of the middle cracks and central center porosity defects in the casting blank. The genetic evolution of protective slag and large size aluminosilicate inclusions is the reason for the two kinds of skin defects.