A few studies have been conducted on the CLS of surface O1s core level for ZnO, in the presence of a certain amount of adsorbed surface H and possible surface defects. However, the effect of H coverage was not studied in depth, even though this is of significant importance for CLS. More importantly, point defects in bulk, which account for the majority of defect peak in XPS, have not been involved. Here, we have investigated the most commonly cited sources in ZnO for the O1s core level spectrum, including surface O and -OH species at the surface with different H coverages, while in the bulk, we include O interstitial (Oi), O vacancy in the +2 charge state (Vo 2+ ) and in the neutral state (Vo 0 ). The lattice relaxation, electronic structures and CLS of these defects have been systematically studied. The O1s core level spectrum is simulated and the binding energy shift (Δ B.E.) is extracted. Comparison with experiments is made to gain a deep insight into the correlation between specific local structures and spectrum features, which is crucial for accurate analysis of defects by XPS. Most notably, our results suggest that the widely adopted assignment in defect analysis, which links the commonly observed defect peak by XPS to the most stable defect (Vo) in ZnO, is very likely a misinterpretation and the origin of the feature is more likely due to Oi or specific -OH surface species.