The influence of the concentration of ammonium dichromate in the postprocessing on the DE of methylene blue sensitized gelatin (MBG) is investigated. The UVand IR spectra show no serious difference between the exposed films with and withoutdichromated post-processing. Little content of chromium is discovered in the X-ray spectrumof the exposed MBG. On the basis of these results, the mechanism of the formation of thehologram is discussed.