Based on the mechanism of the water adsorption of the gelatin material and the experimental results concerning the degeneration of the gelatin holograms in damp environment, a water adsorbing and gelatin hologram degenerating model (WAGHDM) is proposed. The WAGHDM is used to give mechanism explanation for several experimental results about the degeneration of the gelatin holograms. The results show that it can give right explanation is valuable to the work of improving the environment stability of the gelatin hologram.