Active Contours, or snakes, are widely used for segmentation of medical images. This paper presents an automatic active contours model which can extract multiple objects in an image without any manual assistance. Initialization of contours depends on some points which we called centers of divergence. These points are computed by Gradient Vector Flow field. One active contour is generated according to each center of divergence. After normal deformation, we get desired contours as well as some undesired. By an external energy criterion, these contours locate in true boundaries are sought out. All the processes above are performed only by the computer itself