An　explicit　relation　between　the　Bragg　shift　of　the　grating　readout　angle　and　the　shrinkage　of　photopolymer　samples　is　presented　based　on　the　changes　in　amplitude　and　direction　of　the　grating　vector,　caused　by　lateral　shrinkage　and　thickness　shrinkage　of　photopolymer　after　exposure.　A　two-step　experimental　method　to　measure　the　Bragg　shift　of　the　unslanted　grating　and　slant　grating　in　photo　polymer　separately　is　designed　and　implemented　with　blue　light　readin　and　red　light　readout.　The　lateral　shrinkage　and　thickness　shrinkage　of　two　self-made　blue-light　photopolymer　samples　are　calculated　respectively,　and　their　volume　shrinkage　are　obtained.　The　results　show　that　the　volume　shrinkage　of　the　sample　with　modified　composition　is　less　than　0.5%.　This　study　also　shows　that　the　lateral　shrinkage　of　photopolymer　is　generally　not　negligible.　By　using　this　method,　it　is　easier　to　measure　the　shrinkage　of　a　large　amount　of　photopolymer　samples,　and　find　the　relation　between　shrinkage　and　compositions　of　photopolymer.