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At present, most of the references just give a frame pitch of 20 in as an empirical value, but no more other analysis about the reason of the pitch and the influence factors of the frame pitch. The frame pitch is taken as a parameter, the fuselage strength and stability as constraints and the fuselage weight as objective function to make an analysis of the frame pitch, and give a method that how the frame pitch can be designed. And with that method the 20 in frame pitch is verified for aircraft of 150 seats. Meanwhile, the section parameter of the frame and its influence on the skin stress are analyzed by finite element analysis(FEA) and design of experiment(DOE), and a feasible region for the section parameter of the frame is given. The result shows that the value calculated by this method is in good agreement with the empirical value(20 in) for the aircraft of 150 seats. By using FEA, the height of frame should be 80~95 mm, the width of inner flange and outer flange should be 15 mm. By DOE analysis, the width of frame outer flange should be bigger than the inner flange.