Dicyandiamide　is　a　dimer　of　cyanamide　that　generally　isomerizes　into　imino　and　amino　forms.　The　behaviors　of　tautomeric　dicyandiamide　adsorbed　on　gold　surface　were　studied　by　the　density　functional　theory　method　combined　with　surface　enhanced　Raman　spectroscopy　(SERS).　By　using　DFT　method　the　energies,　molecular　orbital,　vibration　spectral　information　of　imino　and　amino　forms　of　dicyandiamide　and　the　SERS　spectra　of　tautomeric　dicyandiamide　adsorbed　on　Au　clusters　were　given.　The　results　show　that　both　tautomeric　dicyandiamides　form　stable　complexes　with　Au3　clusters,　and　the　N(2)　atom　preferentially　adsorbs　on　Au　clusters.　The　experimental　results　are　consistent　with　the　calculated　results,　which　show　that　the　tautomeric　dicyandiamides　coexist　on　the　Au　substrate,　are　adsorbed　vertically　on　the　gold　surface　through　the　N(2)　atom,　and　the　SERS　enhancement　factors　conform　to　electromagnetic-field　enhancement　mechanism.　©Editorial　office　of　Acta　Physico-Chimica　Sinica.