Based on general preparation process of surface-enhanced Raman scattering (SERS) substrate of graphene-silver nanoparticles composites, the coupling agent has been used to improve the uniformity of silver nanoparticles adsorbed on the target substrates; bilayer of polymethylmethacrylate (PMMA) has been used to transfer graphene in order to reduce the defects of graphene; annealing treatment has been used to reduce the Raman background noise and improve the contrast of Raman spectra. The experimental results indicate that using the optimized preparation process can improve the uniformity of SERS substrate. The contrast of graphene Raman signal at G and 2D peak increased by 54.9% and 64.3%, respectively. The goodness of fit (R2) on the relationship between Raman intensities of Rhodamine 6G (R6G, at 774 and 1 363 cm-1) and concentration achieved 0.997 5 and 0.986 7, respectively.