Currently, the thinning algorithms based on the template have no completeness, so there are more error-retention and error-deletion pixels in their thinning results. In this article, using the highest rectangle which can not be eliminated, we put forward a new image-skeleton-extraction algorithm. Because the highest rectangle has completeness, there are no error-retention and error-deletion pixels in its thinning results. The algorithm can effectively eliminate the fracture phenomenon that is generated in the traditional algorithm. At the same time, the skeleton-thinning width is only one pixel, and it achieved to the ideal state. Experiments proved that the thinning result of this algorithm is more effective, and its operational efficiency is better.