The　fixing　phase　of　the　two-center　holographic　recording　is　not　consistent　with　the　mono-exponential　formula,　and　the　charge-transfer　mechanism　of　the　fixing　phase　is　studied　theoretically.　The　electron　gratings　of　the　shallower　traps　center　have　a　great　influence　on　the　fixed　space-charge-field,　the　stronger　electrons　grating　of　the　shallower　traps　center　would　enhance　the　saturation　space-charge-field　of　the　deeper　traps　center　in　the　fixing　phase.　The　effects　of　the　Fe　concentration,　Cu　concentration　and　the　oxidization-reduction　state　of　the　crystals　on　the　fixed　space-charge-field　are　investigated　by　using　the　Runge-Kutta　method.　The　results　show　that　the　higher　Fe　concentration,　the　lower　Cu　concentration　and　the　weakly　oxidized　crystal　are　available　for　enhancing　the　saturation　space-charge-field　of　the　deeper　traps　center.