This article presents an optimization problem of a large aircraft composite wing subject to structural strength. The investigation demonstrated a design optimization process based on a preliminary design of the wing structure. The optimization process was performed by the commercial software OptiStruct, an efficient, accurate and independent finite element solver, which was widely employed in aerospace industry. According to the design objective, the laminate ply thickness of the wing skins were taken as design variables. The optimized structure weight was reduced by 25.07%. A post-process was performed to trim the optimized skin laminate layup and ply thickness under the manufacturing constraint. For a conservative design, an option of increasing the skin laminate thickness was made and led to a slight increase of the weight. However, the final weight saving was still over 20%. A practical optimum process of the composite wing structure with significant weight saving can be achieved by a practical approach and be applied to static strength evaluation in the wing design stage.