Using　the　geometric　configuration　optimized　from　ab　initio　calculation,　the　electronic　structures　of　Cl-2　adsorption　on　MgO(001)　defective　and　irregular　surfaces　were　studied　by　EHT　crystal　orbital　method.　The　characteristics　of　bands　have　been　discussed.　The　results　of　the　optimization　have　proved　that　Cl-2　is　preferable　to　bind　over　oxygen　sites.　Moreover,　Cl-2　binds　at　Mg(3C)　cations　corner　sites　considerably　stronger　than　at　regular　Mg(5C)　and　Mg(4C)　sites.　The　charge　re　distributions　in　the　Cl-2　molecule　and　in　the　substrate　are　considered.　The　magnesium　vacancy　of　MgO(001)　surface　is　more　beneficial　to　Cl-2　adsorption　and　decompose　on　the　surface　than　other　configurations.　It　is　proved　that　the　interactions　between　the　Cl-2/surface　are　weak　physisorption.