A proper excitation wavelength and strong hot-spot effect are of great importance for the application of surface-enhanced Raman spectroscopy (SERS) in the field of biochemistry. As a popular SERS substrate, noble metal nanoparticles dimer is analyzed systematically in this paper. The hot-spot effect and the resonance peak position with varying geometric parameters of metal nanoparticles are investigated. Moreover, the excitation wavelength of bimetallic structure is discussed as well. The conclusions can provide reference for the selection of metal material at different excitation wavelengths.