First-principle calculations were performed to explore the initial reduction of CO₂ on perfect and O-defective CeO₂ (111) surfaces via direct dissociation and hydrogenation, to elucidate the product selectivity towards CO, COOH, or HCOO. The results showed that CO₂ prefers a bent configuration with the C atom of CO₂ occupying the oxygen vacancy site. Reductive hydrogenation CO₂ + H → COOH* was more competitive than CO₂ + H → HCOO* on both perfect and O-defective CeO₂ (111) surfaces. Comparatively, CO₂ hydrogenation towards COOH was slightly more favorable on the perfect surface, whereas reductive dissociation of CO₂ was predominant on the O-defective CeO₂ (111) surface. Electronic localization function, charge density difference, and density of states were utilized to analyze the effect of charge accumulation and redistribution on the adsorption and reductive dissociation of CO₂ caused by the presence of O vacancies. The results of this study provided detailed insight into the initial reduction mechanisms of CO₂ towards different products on perfect and O-defective CeO₂ (111) surfaces.