Abstract: The geometric parameters of the thin section which shape is very complicate usually are substituted by that of the simplistic shapes. Sometime it would conduced to great error. The complicate thin section is divided into finite segments. The formulas of geometric parameters of it are carried out depending on the theory of integral and analytic geometry. The center of figure, twist and flexure are fixed precisely. The moment of inertia can be calculated precisely. The practice indicated that this development can contribute to the shape optimization of the thin sections by changing the positions of the notes.

Key words: Center of flexure, Geometric parameters, Shape optimization of section, Thin section