The effect of different reflector packaging materials and different coupling modes with Si-PM on the light output and energy resolution of Ce∶GAGG and CsI(Tl) scintillation crystals were studied. The transmittance and decay time of Ce∶GAGG and CsI(Tl) scintillation crystals were compared. The experimental results show that the light collection efficiency of Ce∶GAGG and CsI(Tl) scintillation crystals can be improved by optimizing the reflector material and coupling mode. The light output, energy resolution, transmittance and decay time of Ce∶GAGG scintillation crystal are better than those of CsI(Tl) scintillation crystal. The test shows that the best energy resolution of 137Cs radiation source is 4.89% at 662 keV for the Ce∶GAGG crystal sample that encapsulated with TiO2 reflector material and coupled with silicone grease.