Brazing diamond grits to steel substrate using Ni-based filler alloy was carried out via laser in an argon atmosphere. The brazed diamond grits were detected by scanning electron microscopes (SEM),X-ray diffractomer (XRD) and X-ray energy dispersive spectroscopy (EDS). The formation mechanism of carbide layers was discussed. All the results indicate that high strength bonding between diamond grits and the steel substrate has been successfully realized because the chromium in the Ni-based alloy segregated preferentially to the surface of the diamond to form a chromium-rich reaction product Cr3C2,and the bond between the alloy and the diamond is established through the reaction product.