Penicillin sulfoxide ester is an important intermediate of synthesis of GCLE. Firstly the crude peniciuin suifoxide ester was synthesized with toluene as solvent, acetic acid peroxide as oxidant by esterification and oxidation reaction. Secondly through dissolution of the crude product and recrystallization, the target product was obtained with penicillin G as raw material.The results showed that the product content was increased to more than 95%,the total yield reached 91.81%, this process was simple, could improve the product quality, be suitable for industrial production.