Abstract: The diamond was brazed at 1 040 ℃ for 5 min in vacuum by using two kinds of mixed metal powder with different proportion of CuSnTiNi. The microstructure of the interface and brazing alloy was analyzed by SEM, EDS and XRD. The results show that the suitable active ingredient for brazing diamond is BCu70Sn15Ti10Ni5 (mass fraction,%). The brazing alloy can be alloyed in brazing process, and there is TiC formed intermittently on the surface of the diamond, which helps realizing high strength bonding with the diamond. The thermal damage to the diamond is small. The microstructure of the brazing alloy is made up with such phase compositions as α-Cu solid solution and δ-Cu₃₁Sn₈, and the hardness of this brazing alloy is 130~180 HV_0.1, which is higher than CuSnTi.