Series of aromatic formaldehydes (ketones) were synthesized via the oxidation of aryl methyl alcohols in the presence of the combination of 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) and O2. Through screening the reaction conditions, the optimum conditions were obtained as follows: the moles ratio of aryl methyl alcohols and [EMIm][OAc] is 1/1, O2 pressure 0.2 MPa, reaction temperature 130 ℃, and reaction time 12 h. Under the optimal conditions, the gram-scale preparation of benzaldehyde was realized, and 20 aromatic ketones (formaldehydes) products with yields ranging from 65% to 96% were obtained. Moreover, according to related studies and in combination with the results of control experiments, the oxidation reaction mechanism was reasonably proposed: anion [OAc] of [EMIm][OAc] activated benzyl alcohol, O2 oxidation and dehydration to form benzaldehyde.