Abstract: In order to solve the problem that the defect area divided by the Flooding Algorithm is larger than the real one, this paper is to discuss the basic principles and settlement methods of the Active Contour Models(ACM). The ACM is improved and can be located outside the target edge. And the formula can memorize the orientation of edge. When two defects are close to each other, the ACM will constringe along the appropriate edge. Interpolation Algorithm is proposed to interpolate on inconstant edge in order to obtain close edge. The results show that using the ACM can make the initial edge gained by the Flooding Algorithm more precise. The organic combination of these two kinds of Algorithms can detect accurately the surface defect edge of apples.