In　this　paper　we　study　the　dynamics　of　refractive　index　modulation　in　a　dual-monomer　photopolymer　through　grating　growth　under　different　experiment　stages.　By　using　different　sets　of　parameters　for　vinyl　monomers　(NVC)　and　acrylate　monomers　(POEA)　respectively,　a　composite　dual-monomer　model,　extended　from　the　uniform　post-exposure　(UPE)　model　for　single　monomer　photopolymer,　is　proposed　and　fitted　with　the　experiment　data　very　well.　Further　discussions　indicate　that　the　dominant　contribution　to　the　total　index　modulation　is　made　by　NVC　monomers,　and　a　brief　explanation　of　the　function　of　POEA　monomers　is　given.