Abstract: An optimization method is proposed to study the flap track location of the large civil aircraft,in order to meet the design requirements of the stiffness and the deformation. First, with the proper engineering simplification of the flap based on the characteristics of the flap structure and the load, the form of support is determined. Then, according to the basic theory of structural mechanics, the flap stiffness is calculated. Based on the deformation coordination under the load, a optimization model is established. The paper offers a method also for other control surfaces.