The electronic structures and absorption spectra of PWO crystals containing interstitial oxygen ion were calculated using code CASTEP based on density functional theory with lattice structure optimized.It is shown that: the interstitial oxygen ion in the perfect PWO crystal doesn't cause any absorption in the visible region;the green emission of lead tungstate origin is closely related to the interstitial oxygen ion,and probably originates from the center of WO4 Oi.