The optical isomerism reaction of two kinds of the most stable configurations of methionine molecules with amino group as proton transfer bridge were explored by using the B3LYP method of density functional theory and the MP2 method of perturbation theory. The study of reaction process showed that optical isomerism of configuration 1 goes through 2 elementary reactions and configuration 2 goes through 5 elementary reactions. Calculations of potential energy surface pointed out that the stepdetermining of configuration 1 is first elementary reaction and configuration 2 is second elementary reaction. The stepdetermining energy barriers are 124.4 and 128.7 kJ·mol

-1

in gaseous water environment and they are 104.91 and 105.2 kJ·mol

-1

in liquid water environment

respectively

far lower than the energy barriers of 264.2 and 266.1 kJ·mol

-1

in the bare environment. The apparent activation energies are 140.8 and 155.0 kJ·mol

-1

in gaseous water environment and they are 97.9 and 98.9 kJ·mol

-1

in liquid water environment

respectively. The results showed that water molecules and water solvents have good catalytic effects on the optical isomerism of methionine molecule the in proton transfer process. The methionine can be damaged in water environment. The optical isomerism of methionine molecule can be slowly realized in liquid water environment.