Since D. Post promoted the holographic moire' interferometric techniques. It has been developed in all kinds of aspects. It is applied in measuring mechanical parameters in the fields of fracture mechanics, composite material mechanics, biomcchanics etc. Howerver, some problems in the development of the holographic grating and holographic moire' techniques theory are still existed. This paper deducted the frequency of holographic grating and the equation of moire/ method's displacement with Fourier opticsal, and improved the holographic moire' technologic theory. It provides a theoretic foundation for extensive applying of the holographic moire' techniques.