The Bi doped tungstate of cadmium crystals were O2-annealed at various temperature, and the absorption and emission spectra of O2-annealed Bi doped tungstate of cadmium crystals were investigated. The absorption intensity decreased, and the absorption side band was shifted to blue short wavelength as the increase of annealing temperature. The emissions at 528 nm and 1 078 nm were observed under excited by 373 and 980 nm, which they were attributed to the intrinsic emission of CdWO4 crystal and emission of Bi5+ ion, respectively. After the crystals were O2-annealed, the 528 nm emission intensity enhanced while the 1 078 nm intensity reduced. It was attributed to the transformation of Bi5+ to Bi3+ ions in the annealing process. After O2-annealed, the transmission of the crystal was enhanced obviously and the color of the crystal became weak. It is attributed to the decrease of oxygen vacancy (Vo) in crystal after the crystal was heated in O2 atmosphere. The 1 078 nm emission intensity reduced while the 528 nm intensity enhanced after the crystals were gamma-irradiated. It may be due to the transormation of Bi5+ to Bi3+ ions through evolution of gamma-irradiated.