Abstract: The high-strength bonding between diamond grit and steel matrix was realized by using Ni-Cr filler metal under controlled brazing technique. The interface between Ni-Cr filler metal and diamond, also the forming mechanism of carbide layer between filler and diamond surface under the condition of vacuum heating were analyzed by using SEM, EDS and X-ray diffraction. Results show that Cr and small quantity of Si of the Ni-Cr filler metal are accumulated on the diamond surface. Meanwhile, the carbide of Cr₇C₃, Cr₃C₂, and small quantity of SiC are formed by reacting among Cr,Si and C of the diamond. Especially, the Cr₃C₂ distributes as flake on the diamond surface and the Cr₇C₃ distributes as needle-like on the top of Cr₃C₂. As a result, metallurgical bonding is produced between filler metal and diamond through the forming the serial of diamond-SiC-Cr₃C₂-Cr₇C₃ between the interface of diamond and filler metal.