The　first-principles　density　functional　theory　(DFT)　and　self-consistent　periodic　calculation　were　used　to　investigate　the　methanol　adsorption　on　An(111)　surface.　The　adsorption　energy,　equilibrium　geometry,　and　vibrational　frequency　of　CH3OH　on　four　possible　sites　(top,　hcp,　fcc,　and　bridge)　on　Au(111)　surface　were　predicted　and　compared　with　the　experimental　data.　In　the　equilibrium　adsorption　models,　the　O-H　and　O-C,　bonds　are　elongated,　and　the　stretch　vibrational　frequency　is　red　shifted.　Meanwhile　the　O-H　bond　is　activated　greatly.　On　all　the　four　sites,　the　electron　transfers　from　methanol　to　the　metal　surface,　and　the　favorite　adsorption　occurs　at　the　top　site.　The　possible　decomposition　pathway　was　investigated　with　transition　state　searching　by　using　complete　LST/QST　methods.　The　calculation　results　prove　that　decomposition　of　methanol　to　methoxy　and　hydrogen　occurs　on　the　Au　(111)　surface　I　which　is　in　agreement　with　the　available　experimental　results.　The　favorite　adsorption　sites　for　methoxy　and　hydrogen　are　bridge　and　fcc　sites,　respectively.