It is hard for level set method to segment an image with slight topological structure. By analysing the phenomenon, a new method based on dual level sets has been introduced. With this new method, objects can be segmented quickly. Meanwhile, typical level set method can not get the true segmentation when it segments an image with strong noise or week boundary, for it only uses edge information to construct the speed function. So the region information is employed to construct the speed function. Better results are achieved in the application of this method on segmentation of synthetic or cardiac magnetic resonance images.