We have previously reported a second dielectric relaxation ascribed to [2Repb-Oi] in Re-doped PbWO4 (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.