Abstract: The photolytic properties of pinoxaden under different conditions were investigated under the irradiation of a xenon lamp. The results show that the photodegradation of pinoxaden in various organic solvents conformed to the first-order kinetics. The photolysis rates descended in the order of acetonitrile, n-hexane, methanol and acetone, in which the half-lives of pinoxaden in these solvents were 9.76, 15.1, 31.5 and 138 h, respectively. The addition of NH₄⁺ and NO₃^- at 1 mg·L^-1 significantly increased the photodegradation rate of pinoxaden in aqueous solution, with the shortest half-life of pinoxaden as 3.17 h. The sensitization effect induced by these ions reduced as the concentrations further increased. Both Fe³⁺ and Cu²⁺ had a photoquenching effect on the photodegradation of pinoxaden, with a quenching rate up to 16.7%. The photolysis rates of pinoxaden in water were accelerated with increasing concentrations of H₂O₂ and TiO₂. PNDA was used as a hydroxyl radical indicator to confirm that H₂O₂ and TiO₂ both promoted the generation of hydroxyl radicals to accelerate the photodegradation of pinoxaden.