In this study, the defect associated with oxygen vacancy VO in lead tungstate crystals(PbWO4), was investigated by the relativistic self-consistent discrete variational embedded cluster method. We focused on the density state and the effect of color centre induced by VO on the surroundings. The results showed that, VO could produce the WO3+F+ defect in the crystal, and the existence of F+ could result in the absorption of 420nm. In addition, there was not F centre in the PbWO4 crystal.