Through the B3LYP-D3/6-31G(d,p) method of density functional theory (DFT) and using intrinsic reaction coordinate (IRC) to confirm its connected reactants and products, the reaction paths of polyphenylene sulfide (PPS) oxidation were explored by looking for the transition state of sulfoxide and sulfone structure from PPS oxidized by NO2 and SO3. The change of the geometric structure and charge of the middle molecule revealed the microscopic mechanism of NO2 and SO3 oxidation PPS filter material. It showed that part of the electrons were attracted by the benzene ring and O atom when oxidizing S atom, which weakened the bond orders of the C-S bond and made it easier to break. It also increased the aromaticity of the benzene ring, making it easier to undergo substitution reactions and be attacked by free radicals. On this basis, the free energy barriers during the PPS oxidation process at different temperatures were further calculated. The ability of NO2 and SO3 to oxidize PPS was quantitatively compared by the reaction rate constant. Finally, the difficulty of the reactions were compared by calculating the half-life. The calculation results showed that the oxidation ability of SO3 to the S atom in the PPS molecular chain was stronger than that of NO2; in the actual environment, NO2 may not directly oxidize PPS, there were additional reaction paths; the half-life of sulfoxide formation was less than 2.5 h and the half-life of sulfone formation was less than 20 days when sulfur trioxide was less than 5 mol/L, therefore SO3 had a strong oxidizing effect on PPS, and the concentration of SO3 need to be strictly controlled in the environment using PPS.