In　this　work,　adsorption　energies,　geometrical　and　electronic　structures　for　adsorption　systems　of　O-2　at　metal-loaded　graphene　(M-Gra)　and　metal-loaded　defective　graphene　(M-D-Gra)　(M　=　Ni,　Pd,　Pt　and　Al)　surfaces　are　studied　using　a　GGA-PW91　method.　Calculated　results　show　that　loaded　M　make　the　interaction　between　O-2　and　the　graphene　surface　change　from　physical　to　chemical　adsorptions,　band　gaps　of　M-Gra　systems　after　the　O-2　adsorption　change,　and　the　Ni-loaded　Gra　has　the　highest　sensitivity　to　O-2.　For　O-2-M-D-Gra　systems,　interactions　between　O-2　and　the　M-D-Gra　surfaces　are　chemical,　similar　to　the　O-2-M-Gra　systems,　and　loaded　Pt　and　Al　have　the　strongest　effect　on　the　sensitivity　of　D-Gra　to　O-2　.　The　M　loads　at　the　perfect　Gra　and　D-Gra　surfaces　make　the　interactions　between　O-2　and　the　surfaces　have　obvious　charge　transfer.　This　work　would　provide　a　valuable　guidance　on　the　gas　sensitivity　study　of　graphene　to　O-2.