A method of obtaining graphene coated bimetallic nanoparticles used as surface enhanced Raman scattering (SERS) substrates is put forward, by which graphene grows on two-layer metal films in-situ by chemical vapor deposition (CVD) method. The morphology, Raman spectra and probe moleculars of substrate are characterized, and the stability and enhancement factor are analyzed. The experiment results indicate that the substrate shows a well-distributed morphology characteristic and remains SERS-active with a long lifetime. The enhanced factor is estimated to be 107. Graphene plays a role in preventing the surface oxidation of Ag and Cu nanoparticles after exposured to ambient air and dramatically suppress fluorescence of the probe molecules. The chemical enhancement of graphene can also help to improve the enhanced factor of substrate.