The　adsorption　of　O2　at　oxygen　vacancy　site　(F,　F+　or　F2+　site)　and　magnesium　vacancy　site　(V,　V-　or　V　2-　site)　has　been　studied　using　cluster　models　embedding　in　a　large　array　of　point　charges　coupled　to　density　functional　method　at　B3LYP/6-31G(d)　level.　The　value　of　point　charges　is　determined　by　the　self-consistent　technique.　The　calculated　results　indicate　that　the　MgO(001)　surface　with　oxygen　vacancies　has　more　excellent　catalyst　structure　contributing　to　the　adsorptive-decomposition　of　O2　in　comparison　with　the　low-coordinated　corner　site　in　the　previous　study.　The　adsorption　energies　for　O2　adsorbed　on　MgO(001)　surface　with　oxygen　vacancies　are　larger　than　those　on　MgO(001)　surface　with　magnesium　vacancies.　Moreover,　the　MgO(001)　surface　with　magnesium　vacancies　hardly　exhibits　catalytic　reactivity　toward　O2　decomposition.　The　Mülliken　charge　analysis　illustrates　that,　for　O2　adsorption　on　MgO(001)　surface　with　oxygen　vacancies,　the　electrons　are　transferred　from　the　substrate　to　the　adsorbed　O2　and　occupy　the　anti-bonding　orbital,　π*　of　O2.　Thus,　the　O　-　O　bond　strength　is　weakened.　Potential　energy　curve　shows　that　the　energy　barrier　is　considerably　decreased　for　O2　adsorbed　at　oxygen　vacancy　site　of　MgO(001)　surface　when　compared　to　that　at　corner　site　in　our　previous　study.