We reported a green photoluminescence (PL) emission associated with a blue photo-stimulated luminescence (PSL) phenomenon in CaAl2Si2O8 (CASO): Tb3+, Dy3+. With increasing concentration of Dy3+, a great enhancement of the blue PSL attributed to the defects and the transition of Tb3+ is observed. TL spectra indicates that the establishment of trap level introduced by codoping Dy3+ is the reason for the color variation between PSL and PL in CaAl2Si2O8: Tb3+, Dy3+. The trap level not only serves as self-excitation state but also hinders the nonradiative relaxation processes between D-5(3) and D-5(4) state of Tb3+. The result suggests that the introduction of appropriate trap level could provide a promising approach for controlling the color of electron trapping materials (ETMs).