The method of optimization theory based on dual method was transplanted to design fuselage main frame, and the optimizing model of fuselage main frame was established. The target function is the weight of fuselage main frame. There are three kinds of constraints: dimension, strength and flexural rigidity constraint. The program(SAAOP) based on optimization theory was designed. The numerical results show that the structural strength after fuselage main frame was optimized is fit, all so the flexural rigidity...