The catalytic effects of N—hydroxyl phthalimide combined with various transition metal salts on the oxidative breakage ofα—O—4 bond of lignin by O2under mild conditions were studied. Benzyl phenyl ether was adopted as the model compound ofα—O—4 bond.It is found that the cupric salts showed the highestpromotion effect on the catalytic activityof NHPI among the soluble cobaltous, manganous, nickel and cupric salts. Oxygen pressure higher than 0.5MPadoes not necessarily enhance the conversion of benzyl phenyl ether, the activation of α—His most likelythe rate-limiting step.A reaction temperature over 110 ℃ would lead to over oxidation of benzyl aldehyde and phenol.Benzyl phenyl ether conversion of37.2% and the total selectivity of benzyl aldehyde and benzoic acidas high as 91.4% were achieved in acetic acid under the conditions of 110℃, 1.0MPa O2,15hours and using 20% NHPI and 2%Cu(NO3)2with respect to the amount ofbenzyl phenyl etheras the catalyst.