In this paper, the representation method of ship hull and the modification and fairing expert system is discussed. In this research, we represent ship hull by normalized B-spline surface. Instead of representing the entire hull by a single surface, we devided it into several parts and represent them seperately. The degrees of continuity between seperate surfaces are normally Gl, and at some places only G 0 is obtainable. It is usually generate B-spline surface from points which consist of mesh in the surface. An algorithm for generating surface from the mesh curves is developed. With it, we can use water line and station line directly to generate the hull surface. For shape modification of the ship hull surface, an object oriented shape modification and fairing paradigm is proposed to overcome the difficulty of flexibility and consistency caused by the complexity of data structures and the relations between data. Upon that paradigm, a test water line and station line modification and fairing expert system is developed and some results are provided.