We have studied the effects of several factors (electrochemical pretreating, potential applied on the silver electrode, and laser illumination of the silver electrode in aqueous electrolyte during the process of elecrochemical oxidation-reduction cycle) on the enhancement of surface enhanced Raman scattering (SERS) spectra. Experiments showed that electrochemical processing of the silver electrode is of benifit to the adsorption of pyridine molecules, and that the potential applied on the electrode and the laser illumination make it possible for pyridine molecules to be adsorbed on the electrode surface. The experimental results are discussed analytically.