A technique of KrF excimer laser gas alloying with pure nitrogen being employed to improve the corrosion resistance of Al/SiC metal matrix composite is reported in this paper. After excimer laser surface treatment, an aluminum nitride contained layer with a few microns thick was formed on the surface of Al/SiC MMC. In this layer, all of the CuAl2 and most of the SiC reinforcement, which were considered to accelerate the corrosion process of Al/SiC composite, were decomposed and absent. The multiple mechanism of excimer laser gas alloying is confirmed to be effective to improve the corrosion resistance of Al/SiC composite.