In order to improve the accuracy of extracted contours and raise calculation speed,this paper presents an improved method based on level set for underwater objects contours extraction.Object evolution subregion,which is determined by the underwater objects detection results,is proposed to dwindle the search region.At the same time,the centers coordinates of initial closed curves of each object evolution sub-region are determined by the location of object-highlight and shadow regions.The contours of object-highlight and shadow regions are extracted by the four-phase piecewise constant Vese-Chan level set evolution functions.Experimental results and analysis of different kinds of real sonar images demonstrate that the method proposed here is highly adaptable and the calculation speed is faster,moreover,it can more accurately extract object-highlight and shadow contours.