Abstract: Pure SrTiO₃, 0.5 mol% and 1.0 mol% vanadium doped SrTiO₃ were synthesized through hydrothermal method (Noted as S-0, S-0.5, S-1.0 successively). Characterizations including XRD、SEM、BET specific surface area analysis、electron paramagnetic resonance(EPR)、XPS、FTIR、UV-vis absorption spectra and PL offered information about structural features and optical properties of as-prepared catalysts. NO photo-oxidation reaction and CO₂ photoreduction reaction were employed to evaluate the photocatalytic activity of the catalysts. As the study results reveale, the visible-light response improves, and the density of oxygen vacancy decreases as vanadium was doped into Ti-site; S-0.5, the SrTiO₃ sample with 0.5 mol% vanadium doping, shows a better catalytic activity than S-0 at the preliminary stage, but its catalytic activity decays subsequently. According to the characterizations and tests, it could be speculated that oxygen vacancy is the active site for the CO₂ photoreduction reaction, and the insufficient of active sites resulting from the decrease of oxygen vacancy after vanadium doping is the key reason for the decay of photocatalytic activity.