Photo-induced reaction processes and factor of Bragg mismatch in the photopolymer for holographic storage were studied. On the basic of analysis of the theory,the relationship of Bragg mismatch and exposure time was deuced. The curve of the experiment indicated that the Bragg mismatch increased with the increasing of exposure time firstly,then reached saturation. The experimental results compared with analysis of the theory and they are fitted well. All those show that the analysis of the Bragg mismatch is reasonable.