The vibrational structure of dimethoate, with its solid state and saturated solutions at acidic and basic conditions, was characterized with combination of means of FTIR and FT-Raman vibrational spectroscopy technology, and the comprehensive information about the dimethoate molecular groups’ vibrational features was obtained. The surface enhanced Raman scattering (SERS) spectra of dimethoate at different concentrations with different acidic and basic conditions, and adsorbed on the substrate’s surface of the core-shell Au/Ag nanoparticles, were also obtained. The adsorption states of dimethoate’s molecule on the substrate’s surface of the core-shell Au/Ag nanoparticles and the effects by the different acid-base conditions were investigated, with speculation of the adsorption mechanism. From the results, νas(NH), νas(CH3), ν(OCN), τ(OCN), ν(P—O), ν(PS), ν(C—C) and δ(P—O—C) are the characteristic peaks of inner dimethoate structure’s vibrations; and the concentration range in which dimethoate could interact with core-shell Au/Ag nanoparticles fully is about 1.0×10-3 mol·L-1 both in acidic and basic conditions. Dimethoate’s molecule interacts with SERS’ substrate surface mainly through P—O—C, OCC, (S—CH2), PS, and CH3 structures; and the effects of dimethoate’s hydrolysis path in acidic and basic conditions on the adsorption are discussed, which give some good references for the research of organophosphorus pesticides’ transformations in different environmental systems.