At present, benzaldehyde is mainly produced in the way of liquid-phase chlorination of toluene followed by hydrolysis. Such method not only pollutes the environment with the discharge of large amount of waste water, but also limits its application into the field of food and medicine due to the existence of chlorides. In this paper, toluene is oxidized to benzaldehyde by air in acetic acid using polyoxometalate supported on activated carbon as a catalyst. The composition and preparation conditions of the catalyst have been explored. The optimum polyoxometalate composition is determined as Na5.1La0.7CoMn0.3Mo11.7O40·22.05H2O@AC by ICP-OES, FT-IR, XRD and TG. The optimum catalyst preparation conditions are pH1=6.3, pH2=3.8, T1=95°C, T2=85°C, activation temperature 220°C and activation time 4 h. The best experimental results are toluene conversion 13.18 %, benzaldehyde selectivity 40.43 % and benzaldehyde yield 5.33 %.