In this work, kinetics of the CH2OO + SO2 ! HCHO + SO3 reaction was studied by ring-polymer molecular dynamics (RPMD). To perform RPMD calculations, multi-reference configuration interaction (MRCI) was first carried out to compute data for constructing potential energy surface (PES) through a kernel regression method. On the basis of the present MRCI calculations, the statics multi-state mechanism involving the lowest-lying singlet excited state (denoted by S 1) was proposed, which is di?erent from the previously proposed mechanism with the lowest-lying triplet state (denoted by T1). Moreover, the present RPMD calculations predicted the rate coe?cient of 3:95?1011cm3 molecule1s1 at the room temperature (namely 298 K), agreeing with the previously reported experimental values. Finally, based on the present calculations, a probable dynamics mechanism was discussed, where the produced HCHO molecule was proposed to be in a vibrationally excited state. This needs further experimental and theoretical observation in the future.