Catalytic　oxidation　technology　is　still　the　mainstream　technology　of　VOCs　treatment　at　present,　and　it　is　of　great　significance　to　study　the　main　active　components　of　catalysts　and　clarify　the　evolution　and　transformation　process　of　intermediate　products　in　the　catalytic　process　for　clarifying　the　reaction　mechanism　and　guiding　the　catalyst　design.　Pd　was　identified　as　the　main　active　component　in　catalytic　oxidation　of　toluene,　and　the　important　intermediate　products　in　the　degradation　of　toluene,　i.e.,　benzaldehyde　and　benzoic　acid,　were　obtained　through　experiment　and　In-situ　DRIFT　spectra.　However,　the　specific　evolution　process　of　intermediates　is　difficult　to　observe　experimentally.　The　conversion　of　toluene　on　Pd　(111)　surface　was　studied　by　DFT　calculation.　Benzaldehyde　was　the　most　stable　intermediate　and　benzoic　acid　was　the　most　stable　energy　state　of　the　reaction　products.　Then　the　activation　energies　and　reaction　energies　of　all　possible　reaction　paths　from　toluene　to　benzaldehyde　or　benzoic　acid　were　calculated,　and　the　only　transition　state　was　obtained.　Two　pathways　for　the　formation　of　benzaldehyde　and　benzoic　acid　were　identified,　in　which　the　oxidation　reaction　after　dehydrogenation　may　be　the　common　rate-determining　step　of　the　two　pathways,　with　a　maximum　energy　barrier　of　0.80　eV.