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We have previously reported a second dielectric relaxation ascribed to [2Re pb-O i ] in Re-doped PbWO 4 (Re=La, Y) after annealing at 750 C. Further investigations by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) have been performed in heterovalent-ion-doped PWO before and after annealing at 850 C. The existence of interstitial oxygen in the Re:PWO is confirmed after annealing in air at high temperature. Heavy doping with trivalent/ tetravalent ion will induce interstitial oxygen ion in the scheelite PWO for charge compensation. Based on the experimental results, we construct a hypothesis to clarify the mechanism of doping at different concentrations and estimate the lead deficiency in as-grown PWO to be around tens at.ppm.