The　interaction　of　atomic　oxygen　with　the　clean　Cu(100)　surface　has　been　studied　by　means　of　cluster　and　periodic　slab　models　density　functional　theory　in　the　present　paper.　The　Cu(4,9,4)　cluster　and　a　three-layer　slab　with　c(2x2)　structure　are　used　to　model　the　perfect　Cu(100)　surface.　Three　possible　adsorption　sites,　top,　bridge　and　hollow　site,　were　considered　in　the　calculations.　The　predicted　results　show　that　the　hollow　site　is　the　prefer　site　for　atomic　oxygen　adsorbed　on　Cu(100)　surface　energetically.　This　is　in　good　agreement　with　the　experiment.　The　calculated　binding　energies　are　respective　2.014,　3.154　and　3.942　eV　for　top,　bridge　and　hollow　sites　at　mPW1PW91/LanL2dz　level　for　the　cluster　model.　The　geometry　of　Cu(100)　surface　has　also　been　optimized　theoretically　with　various　density　functional　methods　and　the　results　show　that　the　prediction　from　the　B3PW91/LanL2dz　and　mPW1PNW91/LanL2dz　reproduce　the　experimental　observation.　The　frontier　molecular　orbitals　and　partial　density　of　states　analysis　show　that　the　electron　transfer　from　the　d　orbital　of　substrate　to　the　p　orbital　of　the　surface　oxygen　atom.