The invention relates to a method for growing graphene by a metal-assisted internal/external carbon sources combination mode on a 6H/4H-SiC silicon surface. The method is characterized in that Si-C bond on the surface of SiC wafer is partially cracked by heating at high temperature, then cooling is rapidly carried out to the growth temperature of a CVD technology, external carbon source is introduced through a metal channel, graphene is continuously grown on the surface of the SiC, and synergism of SiC internal carbon source and external gas carbon source is used for preparing the graphene monocrystalline with large size and high quality. The destroy on graphene during a CVD method transfer process is avoided, influence on a substrate buffer layer is decreased, and the graphene with better quality is obtained.