To clarify the action mechanisms of microwave field with peroxyacetic acid in the process of sulfur removal from coal, this study was carried out on the molecular level and diphenyl sulfide was selected as the sulfur model compound of coal. Its oxidation reaction path was determined utilizing XANES and GC/MS. The transmission reflection method was adopted to analyze the dielectric property of the substances detected before. Their CeS bond dissociation energies (BDEs), bond dissociation times (BDTs) and the intrinsic reaction coordinate of de-sulfurization reactions were calculated under various extra electric fields to support the experimental results. Results showed that most of diphenyl sulfide was oxidized to the corresponding sulfoxide and sulfone, resulting in a desulfurization degree of 22.37% after microwaving treatment at 500W for 120 s combined with peroxyacetic acid. With the oxidation degree deepening, the absorption efficiency of microwave energy for sulfur groups increased and their CeS BDEs decreased, resulting in the reducing of their CeS BDTs. In addition, the CeS BDTs and the barrier of desulfurization reactions were reduced under the extra electric field. These findings confirmed that the sulfur-containing bonds cleavage and desulfurization reactions of sulfur groups were promoted under the extra microwave field with peroxyacetic acid, which is conducive to the effective removal of sulfur groups from coal.