The image binarization effect is unsatisfactory because there are no chromatic differences between the protuberant characters and the background in the industry tag. In this paper,the Canny detector is used to detect the edges of protuberant charactors. A method based on two-step gradient image is adopted to patch the break edges. And Edge-Traching technology is successfully used to patch,the flaw edges detected by Canny operator to make them integrity. The experiment proved that the proposed method has gotten ideal effect.