Methylaminopropyltrimethoxysilane (MAPS) coupling agent was used to pre-modify SrAl2O4:Eu2+, Dy3+ phosphors, and then graft methylmethacrylate (MMA) on SrAl2O4:Eu2+, Dy3+ phosphors. IR, SEM and TEM measurements showed that there is an organic encapsulation film composed of silane modified poly(methylmethacrylate) (PMMA) on phosphor surface. This organic film encapsulated on phosphor surface like dense reticulation with a thickness of 20-30 nm. The water resistance and oil absorption measurements and persistent luminescent properties showed that after being encapsulated, SrAl2O4:Eu2+, Dy3+ phosphors has much better water resistance and lower oil absorption with little loss of persistent phosphorescence. The emission intensity and afterglow lifetime of the encapsulated phosphors were reduced to 93% and 95% of the originals, respectively.