We integrate the detected object shape represented by shape restraint equation(s) and general active contour models into a unified energy function to generate the shape preserving active contour model,which keeps the curve to be a specific class shape in the evolvement.In this model,a specific class contour shape is represented as the zero level line of some certain parametric level set function(s).So,this model can not only detect the given object correctly but also characterize the object shape quantificationally via these parameters.In addition,we build an energy functional for elliptic objects detection using the proposed model,deduce the corresponding Euler-Lagrange ordinary differential equation (ODE(s)) of its shape parameters and implement them using level sets method.The elliptic object detection model has many applications such as papilla segmentation,iris detection and camera calibration.By numerical experiments presented in the paper,it can not only detect the elliptic objects correctly but also is robust to noise,deformity and occlusion etc.