Abstract: The spherical gold nanoparticles were prepared by thermal reduction reaction with gold chloride acid as precursor and trisodium citrate as reductant. The normal Raman scattering (NRS) spectroscopy of caffeic acid (CA) and the surface-enhanced Raman scattering (SERS) spectroscopy of CA absorbed on gold nanoparticles were collected by laser Raman spectrometer. Density functional theory(DFT) method at the B3LYP/6-31+G**(C, H, O)/LANL2DZ(Au) level was used during calculation. The molecular configurations of caffeic acid were optimized firstly. Base on the optimized structure, the NRS spectroscopy of CA and the SERS spectroscopy by possibly three kinds of adsorption configuration of CA adsorbed on gold nanoparticles were all calculated. Comparative analysis showed that the calculation results using CA molecules adsorption configuration through carboxyl and hydroxyl group were matched best with the experimental values. Then the vibration modes of CA molecules were further elucidated in details. The results demonstrated that the adsorption of CA molecules and Au nanoparticles occurs through the interaction between carboxyl and hydroxyl groups on CA molecules. Finally, the determination of the adsorption mode of CA molecules in Au sol was achieved by calculating the molecular frontier orbitals of CA molecules when adsorbed with Au nanoparticles.