A highly reproducible and broad plasma absorption band nano-silver film was prepared by electrostatic self-assembly technology. The size of nano-silver particles on the surface of silver film, in the scanning electron microscopy (SEM) micrograph, is in a wide distribution from 18 to 200 nm. At the same time, the ultraviolet-visible spectrophotometer was employed to detect the nano-silver film. There is a broad plasma absorption band in the UV-Vis spectrum. To test the SERS activity of the nano-silver film, crystal violet and serum of healthy person were used as probe molecules and the high quality SERS spectra were obtained.