Accuracy of the fitted surface is of great importance to the performance of deployable antennas utilized in space. This paper proposes a stiffness analysis based fitting accuracy optimiza-tion method for achieving the optimal parameters of the parabolic cylindrical deployable antenna mechanism. The stiffness matrix of the proposed cylindrical antenna mechanism is established by assembling the stiffness of beams and tension cables. Structural deformations of the mechanism are calculated where the tensioned cable is substituted by a 2-node truss element and an equivalent force acting on the joint. Consideration of the tensity of tension cables, namely tensioned or slack, is transformed into a typical linear complementarity problem. Comparison between structural defor-mations of the mechanism fixed at different points is performed. Sensitivities of the geometric and structural parameters on fitting accuracy are investigated. Influence of force of the driven cable on structural deformations of antenna operated in different orbits is conducted. A fitting optimization method is proposed to minimize the structural deformations subject to constraints on volume and mass. Simulation result shows that the fitting accuracy of the antenna mechanism is improved sig-nificantly through the optimization. The proposed method can be utilized for the optimal design of other deployable mechanisms constructed by joining rigid links.