A new method of synthesis Au/Ag core/shell nanostructure with KrF excimer laser is studied. It is found that the Au/Ag core/shell nanostructures with spherical shell can be prepared by KrF excimer laser which is obviously confirmed by high resolution transmission electron microscopy (HRTEM). The surface plasma resonance (SPR) of this nanostructure can be tuned by controlling thickness of the Ag shell. Simulation based on Mie theory is in agreement with the result of the experiments. Moreover, it is indicated that the Au/Ag core/shell nanostructure has excellent activity in surface-enhanced Raman scattering (SERS). This Au/Ag core/shell nanostructure may be applied to high sensitive trace detection in the future.