Interaction　of　atomic　and　molecular　oxygen　with　perfect　and　defective　Cu2O　(111)　surfaces　has　been　studied　by　periodic　density　functional　theory　coupled　with　slab　models.　Different　kinds　of　possible　modes　of　O　and　O-2　adsorbed　on　Cu2O　(111)　surface　and　possible　dissociation　pathways　were　calculated.　Meanwhile,　different　electronic　states,　i.e.,　the　singlet　and　the　triplet　states　were　considered　in　the　computation.　The　optimization　of　the　geometry,　calculation　of　the　adsorption　energy,　vibrational　frequency　and　analysis　of　the　Mulliken　population　were　carried　out.　The　results　indicate　that　Cu-CSA　site　is　slightly　more　favorable　than　Cu-CUS　for　O　adsorption,　and　for　O-2　adsorption　over　perfect　surface,　Cu-CUS　site　is　the　most　advantageous　position,　especially　for　O-2　with　end-on　type.　For　O-2　adsorption　over　the　deficient　surface,　it　has　a　larger　adsorption　energy　compared　to　O2　adsorption　over　the　perfect　surface　and　the　O-O　bond　strength　is　considerably　weakened　when　O-2　lies　flatly　on　the　oxygen　vacancy　site　and　lies　flatly　over　1-vacancy　bridge　site.　And　the　oxygen　adspecies　is　characteristic　of　a　classical　O-2(-)　ion　on　perfect　surface,　whereas　is　O-2(2-)　ion　on　oxygen-deficient　surface.　The　calculations　for　transition　states　show　that　the　dissociation　reaction　of　O-2　on　deficient　surface　is　highly　exothermic　with　a　very　small　barrier　height.