In order to rapidly and accurately extract regions of interest from a complicated image,by combining the gradient vector flow and the signed-distance penalized functional,an image segmentation method based on adaptive external force is proposed under the variational level set frame.This method correctly attracts the initial contours inside outside,even across the object to the object boundary,introduces the signed-distance penalizing term to avoid complicated and time-consuming signed-distance re-initialization procedure,and employs the weighted arc length-rectifying term to make the contour to evolve continuously and smoothly during the propagation.The proposed me-thod,together with the existing Li＇s method,is finally used to segment hybrid and real medical images,the results demonstrating its feasibility and superiority.