Volatile　organic　compounds　(VOCs)　exists　ubiquitously　in　chemical　industries　and　were　regarded　as　major　contributors　to　air　pollution,　which　should　be　strictly　regulated.　Vacuum　ultraviolet　irradiation　coupled　with　photo　catalytic　oxidation　(VUV-PCO)　has　been　considered　as　an　efficient　approach　to　VOCs　removal　due　to　high-energy　photons　which　could　break　down　VOCs　directly　and　be　absorbed　by　photocatalysts　to　generate　free　radicals　for　further　oxidation.　However,　the　photochemical　transformation　mechanisms　of　VOCs　have　not　been　fully　revealed.　Herein,　we　systematically　analyzed　the　intermediates　using　proton-transfer-reaction　mass　spectrometer　(PTR-MS)　to　explore　the　transformation　mechanisms　of　toluene　degradation　in　VUV　and　VUV-PCO　processes.　VUV-PCO　process　displayed　superior　toluene　degradation　efficiency　(50　%)　and　mineralization　efficiency　(65　%)　compared　with　single　VUV　photolysis　(35　%)　and　UV　photocatalysis　(5　%).　TiO2　was　deeply　involved　into　CO2　generalization　by　amplifying　the　advantages　of　VUV　system　and　further　mineralizing　the　intermediates.　In　VUV　and　VUV-PCO　processes,　O-2　participation　changed　the　intermediates　distribution　by　increasing　multiple　oxygenated　products,　while　the　introduction　of　water　contributed　to　the　formation　and　degradation　of　most　intermediates.　A　possible　degradation　mechanism　of　toluene　under　VUV　irradiation　combined　with　TiO2　was　proposed.　This　study　provides　a　deep　mechanistic　insight　into　VOCs　degradation　by　VUV-PCO　process.