Abstract: The reversibility of the diffraction optical path of grating and double-grating imaging systems was studied with Fresnel diffraction theory. Firstly, the complex amplitude distribution of the diffraction of single grating was analyzed. According to the phase relation of the complex amplitude distribution, the reversibility of optical path was studied. Then the reversibility of the double-grating diffraction imaging effect was analyzed by using the conclusion for the single optical diffraction grating. It-s found that the diffraction optical path of single grating and double-grating imaging systems has partial reversibility. Based on the partial reversibility of diffraction optical path, the nature of double-grating imaging effect was explained, the spectral combination characteristic was considered to be the reverse effect of the spectral dispersion characteristic, and the image processing was realized.