The energy bands of PbWO4 crystal are studied by using discrete variational Xa method. The ground states of both F center and F+ center in stoichiometry PbWO4 crystal are calculated by using the 1S state eigen function of the H-like atom as the trial function. The results show that the ground states of both F center and F+ center fall into the forbidden band of the crystal and situate apart from the bottom of the conduction band 1.97 eV(630 nm) and 2.36 eV(525 nm) respectively. Being excited, the electron of the F center and F+ center can transfer from their ground to the bottom of conduction band forming the F center and F+ center absorption bands respectively. The light irradiation induced absorption spectra of the stoichiometry PbWO4 crystal poccesses a broad band posited between 500~700 nm, which can be decomposed into two Gaussian bands peaking at 550 nm and 680nm respectively. The theoretical results coincide well with the experimental results.