In this paper, we describe a new method for determining 3D-shape of objects which consist of specular plane surfaces. The method uses a light source of grating pattern encoded by an M-sequence. Being reflected by a specular plane and perspectively projected into an image plane, the set of parallel source lines produce a set of image lines converging into a vanishing point. The orientation of the specular plane can be determined by the vanishing point and the slope of the source lines. The position of the plane can be determined by the correspondence between image lines and source lines which is obtained by using a characteristic regularity of M-sequence. The determination of surface planes allows us to reconstruct the specular objects.Simulation and experimental results are shown to verify the analytic expressions. The error in determining plane orientation and depth is discussed. The main advantage of the method is that it needs only one image.