Abstract: In this paper,the working region of a three d.o.f.multi-articulated finger-mechanism is expressed byits workspace and/or attainable space.The volume of the workspace and the area of the singular curvedsurface is formulated by means of the method of analytic geometry.We analyze the existing conditions ofisotropic points of the finger-mechanism and take these conditions as the design constraints.Further,wetake the maximum volume ratio of the workspace and the minimum area ratio of the singular curved surface as the object functions of the optimization design.We see that the maximum volume ratio indicates also the optimal working configuration of the finger-mechanism.Throughout this paper,the A3 type is takenas example,and adequate numerical calculations of it has been given.