Abstract: The microstructure and formation mechanism of the products in the interface of the joint of c-BN brazed to CuNiSnTi filler metal were investigated by scanning electron microscope(SEM), energy dispersion spectrometer(EDS), as well as micro X-ray diffraction(XRD). Also, the growth process and diffusion activation energy of the interfacial reaction products were deeply studied with a kinetics theory. The results showed that the CuNiSnTi filler metal exhibited a good wettability on c-BN in the brazing. And the reaction between filler metal and c-BN occurred, therefore the reliable connection between c-BN andJP2steel substrate was realized. The new phase of Ti-N and Ti-B compounds were found in the interface between filler metal and c-BN. Then the formed structure of the interface was in the form of filler/TiN/TiB/TiB2/c-BN. The growth process of reaction layer depends mainly on the inter-diffusion among the atoms and chemical reaction generated at the interface in the brazing temperature of 1153-1193 K for 5-20 min following a parabolic rule.