Using　the　geometric　configuration　optimized　from　ab　initio　calculation,　the　energy　band　structure　of　CO　adsorption　on　MgO(001)　defective　and　irregular　surfaces　were　studied　by　EHT　crystal　orbital　method.　The　structures　and　components　of　the　bands　have　been　discussed.　By　means　of　analyzing　the　changes　of　bonding,　CO　binds　at　Mg(3c)　cations　considerably　stronger　than　at　regular　Mg(5c)　and　Mg(4c)　sites.　The　charge　redistributions　in　the　CO　molecule　and　the　substrate　are　considered.　It　is　shown　that　CO　may　bind　to　the　surface　with　a　slight　preference　for　the　O-Mg2+-C(CO)　interaction.　The　oxygen　vacancy　of　MgO(001)　surface　is　more　beneficial　to　CO　adsorption　and　decompose　on　the　surface　than　other　configurations.