Using　density　functional　theory　(DFT),　the　adsorption　of　cyanide　(CN)　on　the　different　sites　of　Cu(　100)　surface　was　studied　with　end-on　and　side-on　geometries.　Cu-14　cluster　was　used　to　simulate　the　surface.　The　present　calculations　show　that　it　is　more　favorable　than　other　adsorption　sites　for　the　CN　to　bond　to　the　top　site　via　carbon　with　the　molecular　axis　perpendicular　to　the　surface.　The　calculated　C-N　stretching　frequencies　are　red-shifted,　expect　CN　adsorbed　on　the　top　site　via　carbon.　For　CN　bonded　to　the　surface　via　the　carbon,　the　results　of　the　density　of　states　(DOS)　and　the　charge　analysis　show　that　there　are　a　strong　a　bonding　and　a　weak　pi　anti-bonding　between　Cu　and　CN　molecules.