In order to obtain the self-lubricating and antiwear composite coating with high hardness for tribological metal surfaces, especially for line—or point-contact surfaces, the technique and microstructure of the laser alloying coating of Si 3N 4/graphite composite materials on 45 # carbon steel, and the interface between the coating and substrate are studied. The distribution and content of the elements in the alloyed coating are examined and analyzed with OM, SEM and EDS, and the micro-hardness along the depth is measured. Results show that silicon nitride in the coating decomposes completely during laser scanning, but Fe, Co, Si and C distribute evenly on the cross section and the content of C reaches 15.69%. The existing form of most C is graphite, which has self-lubricating property. At the same time, the surface micro-hardness has been improved by solid solution mechanism of Si-Fe, Co-Fe and martensite.