Based　on　two-center　model,　multiplexing　of　nonvolatile　holograms　with　equal-time　exposure　in　LiNbO3:Fe:Cu　crystals　was　simulated　by　using　Runge-Kutta　method,　and　the　physical　mechanism　of　equal-time　multiplexing　was　analyzed.　Considering　both　the　mechanisms　of　optical　erasure　and　varied　diffraction　efficiency,　equal　exposure　time　can　compensate　for　the　gradual　decrease　of　sensitivity　when　recording　latter-recorded　holograms　and　holograms　with　nearly　equal　diffraction　efficiencies　can　be　achieved.　The　optimization　of　multiplexing　holograms　with　higher　diffraction　efficiency　was　discussed,　when　intensity　ratio　of　red　beams　to　UV　beam　I-R/I-UV　is　about　15,　the　maximum　of　the　average　diffraction　efficiency　can　be　obtained.　(C)　2015　Elsevier　GmbH.　All　rights　reserved.