The removal efficiency of Prometon degraded by O3/H2O2 advanced oxidation process (AOP) was represented by the pseudo-first-rate order to discuss the effect of n(H2O2)/n(O3), pH, water quality and HCO-. The organic products were characterized by GC/MS and LC/MS and NO3- produced during degradation was determined by IC, on the basis of which the degradation path of Prometon was also investigated. The result indicated that when concentration of Prometon was 2 mg x L(-1), dosage of ozone was 13 mg x L(-1), the reactive temperature was 25 degrees C, the optimal condition of degradation was as follows, n(H2O2)/n (O3 ) = 0.7, pH 7-8; The micro inorganic and organic substances in tap water promoted the removal rate of the Prometon comparing to that in pure water, and HCO3- showed inhibition effect on degradation. The results of GC/MS and LC/MS suggested that the triazine ring of Prometon was not destroyed during the AOP, the two isopropyl of triazine ring were disengaged firstly, and the NO3- detected by IC might be the oxidation product of the amido of the triazine ring.