In this paper, the hydrolysis mechanism of monosulfuron herbicide was studied by B3LYP method at the level of 6-31G*. The geometric configurations of reactants, products, intermediates, and transition states in the reaction have been optimized and vibrational analysis has been performed. The results of calculation show that in the basicity, the reaction channel has one five-membered ring transition state TS1, with the activation energy of the controlling step during the reaction of 25.7 kJ/mol, while in the neutrality, the reaction channel has one three-membered and two four-membered ring transition states, and the controlling step is M3'＋H₂O→TS2' during the reaction with the activation energy of 236.5 kJ/mol. That is to say, the hydrolysis reaction of monosulfuron herbicide proceeded more easily in the basicity than neutrality, which is essentially consistent with the experimental result. Besides, the influence of the solvation effect was also discussed.

Key words: monosulfuron, hydrolysis mechanism, basicity, neutrality