Fiber laser brazing diamond grains to substrate using Ni-Cr filler alloy was carried out in an argon atmosphere. The effects of laser power and welding speed on the weld appearance were analyzed. The microstructure and compound of Ni-Cr filler alloy and diamond grains brazed interface were studied. The results show that the laser power and welding speed have a significant effect on the degree of melting of Ni-Cr filler alloy and the thermal damage of diamond. Lower laser power and welding speed made a poor weld appearance of the brazed joint. A good weld appearance was obtained when the laser power and the welding speed were larger, however, the Ni-Cr filler alloy at the bottom of the diamond grains was insufficiently melted, resulting in fall off of the diamond. When the range of the laser power was 700 W~760 W, the welding speed was 0.7 mm/s~1.5 mm/s, and the defocus value was +18 mm, the brazed joints with good weld appearance and high bonding strength were obtained. There was a thin bonding interface between the Ni-Cr filler alloy and the diamond grains, with thickness of ~4 μm. There were slice-like and acicular products on the surface of the brazed diamond grains. The result of XRD analysis indicated that the compound on the brazed diamond grains was Cr3C2.