The method for converting from line segment form to chain code form is improved to solve the defects of the existing one. In the original method, 6 kinds of segments were proposed according to the different characteristics of the line and converting them to chain code by their types. This works only for the general situations. When the specials such as the target are only one pixel width, the segment won’t belong to any one of above categories, and the program will go error or even blow up. Two new kinds of segments are proposed to make up for the deficiencies of the existing algorithm and the detail process of them is provided. Experimental results show that the new method can be the perfect realization of the binary image contour extraction by converting from line segment form to chain code form.