The　mechanism　of　CO　oxidation　on　the　WO3(001)　surface　for　gas　sensing　performance　has　been　systematically　investigated　by　means　of　first　principles　density　functional　theory　(DFT)　calculations.　Our　results　show　that　the　oxidation　of　CO　molecule　on　the　perfect　WO3(001)　surface　induces　the　formation　of　surface　oxygen　vacancies,　which　results　in　an　increase　of　the　surface　conductance.　This　defective　WO3(001)　surface　can　be　re-oxidized　by　the　O2　molecules　in　the　atmosphere.　During　this　step,　the　active　O2−　species　is　generated,　accompanied　with　the　obvious　charge　transfer　from　the　surface　to　O2　molecule,　and　correspondingly,　the　surface　conductivity　is　reduced.　The　O2−　species　tends　to　take　part　in　the　subsequent　reaction　with　the　CO　molecule,　and　after　releasing　CO2　molecule,　the　perfect　WO3(001)　surface　is　finally　reproduced.　The　activation　energy　barriers　and　the　reaction　energies　associated　with　above　surface　reactions　are　determined,　and　from　the　kinetics　viewpoint,　the　oxidation　of　CO　molecule　on　the　perfect　WO3(001)　surface　is　the　rate-limiting　step　with　an　activation　barrier　of　about　0.91　eV.　©　2017　by　the　authors.　Licensee　MDPI,　Basel,　Switzerland.