SrAl2O4:Eu2+, Dy3+ long persistence phosphors are synthesized by microwave plasma method. The effects of molar ratio of Dy3+ and Eu2+ on the phase composition, the spectrum properties and long afterglow property of phosphors are investigated in the paper. The analysis results show that spectrum properties depressed clearly following the increase of Dy3+/ Eu2+. And the afterglow property of phosphors are improved by doping of the Dy3+, but suppressed by excessive doping. On the one hand, this is because that the number of electrons trapped by defect levels increased with the increase of Dy3+. But on the other hand, it’s difficult to occur electric transition if doping excessive Dy3+, so leads to performance depressed. Above-mentioned results, it’s confirm that the optimized Dy3+/Eu2+ molar ratio is 2:1 when SrAl2O4:Eu2+, Dy3+ phosphors synthesized by microwave plasma method.