With the aim of finding the optimum design that maximizes the stiffness of shell structures, an suitable approach for combined shape and topology optimization of free-form surface is presented. For numerical expression for the configuration of free form shell, NURBS (Non Uniform Rational B-Spline) is utilized. For shape optimization, the approach is employed to calculate the differential of total structural strain energy corresponding to surface height parameters. The surface height is adjusted iteratively according to its sensitivity to total structural strain energy. For topology optimization, the OC algorithms which are derived from the necessary optimality conditions are used and element connectivity is taken as design variable. The method has been implemented into a computational 3D model and example is provided to show the applicability of the present method.