Mechanical structure as airborne evaporation circulatory system's main support, has great quality and vibration impact from the helicopter. Its performance affects the normal function of the whole system. On the premise of guaranteeing sufficient strength and rigidity of structure, lightweight design has important theoretical significance and practical value. For analysis of structure design, the actual stress distribution of the structure is well simulated by the method of finite element method (fem) analysis, solving the difficulties of analysis and calculation of complex structure parts, which fundamentally changed the traditional design method of experience. The structure is parametric designed by using real-time transfer function of parameters between Pro/E and Ansys Workbench. The critical dimensions of parameters model are got by using the sensitivity analysis, which have more influence the optimization goal. And then the multi-objective genetic algorithm is adopted to design its structure. The result is that the quality than the original dropped 24.4%. The optimal structure parameters are obtained to realize the lightweight of the structure.