Abstract: The interface of the SiCn/20Cr steel composite material fabricated via vacuum-gas casting process was investigated with XRD and EDS (energy-dispersive spectroscopy analyzer) attached to SEM. The result revealed that an intensive solid-phase reaction occurs on the composite's interface between SiC and 20Cr steel, then SiC decomposed into Si that forms Fe-Si compound with Fe and C that precipitated in graphite form. The solid-phase reaction zone is composed of three zones, i.e. the metal, silicon carbide and carbon precipitation zones. The precipitating form of C in carbon precipitation zone relates to the distance between the precipitation position and silicon carbide. The (Cr, Fe)23C6 and Fe3Si is the products from metal reaction zone are verified by transmission electron microscope (TEM), of which the formation of Fe3Si provides thermodynamically the driving force for the decomposition of SiC.