As the active contour model(Snake model) is widely used in automatic missions

higher robustness and adaptability of the model are required.Due to the contraction

over-flatten effect on contour and scale variance of the traditional model

the adjustment of its parameter is quite difficult and hard to be automatically decided by program.Our constantly changing curvature based internal force model is scale invariant.Besides keeping the smoothness and continuity of the contour

no side effect is introduced and the robustness of model parameters is increased greatly.Experimental results show that the proposed model greatly improves the ability of detecting the accurate contour of the target

and even works well for the contour with high curvature position and concavity.Because of fast attenuation of internal force and insensitivity to addition and deletion of contour points

the model is guaranteed to converge quickly and steadily to the expected contour.