In the present paper, DFT method at the B3LYP/6-31+G**(C, H, O)/LANL2DZ(Ag) level was used to optimize molecular configurations of furfural. Based on the optimized structure, the normal Raman spectrum (NRS) of FUR and the surface-enhanced Raman spectrum (SERS) of FUR adsorbed on Ag, Ag2 and Ag4 were all calculated, which were compared with the experimental values. The calculation results indicated that a good conformity was found between the computed and the experimental results. The results of furfural adsorbed on Ag4 were more approximate to the ever reported experimental date than those of furfural adsorbed on Ag and Ag2. At the end, detailed analysis of the Raman spectrum and more comprehensive assignments of the vibration mode for furfural were studied by the software of GaussView. The data of the SERS by comparing with the one of NRS show that furfural molecule and Ag atoms interact with each other. And we suppose that the molecular plane with the ring of adsorbed furfural molecule is vertically orientated to the silver surface. The work in this paper offers a theory evidence for detection and trace analysis of drinks containing furfural.