Abstract: The Cu-Sn-Ti active filler alloy was utilized to braze CBN(cubic boron nitride) to steel substrate in vacuum furnace.The microstructure and the element distribution,as well as the topography and phases of the compounds were analyzed by optical microscopy,scanning electron microscope(SEM),energy dispersion spectrometer(EDS) and X-ray diffraction(XRD).The results show that the active element Ti migrated from the filler layer to the surface of the CBN grains to form the compounds such as TiN,TiB and TiB₂,which play an important role in the joining of CBN grain and Cu-Sn-Ti alloy.As a result,the layer of TiN+TiB+TiB₂-Cu/Sn/Ti intermetallic compound-Cu/Fe/Sn diffusion layer and Fe/Ti compound were formed between the interface of CBN and metal matrix.