The frame pitch is related to aircraft overall design and structure design. Now most of the references just give a frame pitch of 20in as an empirical value. This article takes the frame pitch as a parameter, the fuselage strength and stability as constraint and the fuselage weight as objective function to make an analysis of the frame pitch, and give a method that how the frame pitch could be designed. And with that method the 20in have been verified for aircraft of 150 seats. Also this article make an impact analysis of the section parameter of the frame to skin stress by FEA and DOE, and give a feasible region for the section parameter of the frame.