This note presents the main process of optimization design of foam core/carbon fiber composite sandwich which primarily designed for UAV wing beams. During the actual application, the original design provided excessive structural strength and it has certain capacity to be optimized. So the weight of structure can be reduced under the premise of meet the strength requirement. In order to characterize fully the complex mechanical behavior of such a highly heterogeneous material and find the ultimate strength of this structure, MSC.Patran/Nastran has be applied on analysis of this composite sandwich structure. Base on the result of the numerical simulations, the best combination of composite laminated and the material layer thickness have be determined, and the beams structure of the lightweight has be designed ultimately.