In this paper，the thin wall stiffening shell is analysed by means of the finite element method，the element stiffness matrix of the bar with the variable axial force is derived，and the method dealing with cross-elements and boundary restraint is presented. The structure is synthesized by means of the full stress method. The pattern of the "synchronized" iteration is used in process of optimization for the elements that are controlled by the pressure stress. At the same time，the necessary geometrical restraint is introduced. The conclusion indicates that the weight for optimized structure is obviously reduced.