Base on theory of lithosphere elastic flexure isostatic compensation, the spheric harmonic series expressions of topography-isostasy compensation gravity and geoid are established.

Based on the simple beam theory, it analyzes the vibrancy character of straight-leg flexure structure, and derives the practical formula of this structure to calculate the resonance frequency.

Taking a heliostat as example, the paper applies thin plate flexure theory and study regularity of load-deflection curve for reflector plate.