Abstract: Vacuum brazing of diamond and hard alloy were performed using Ag72-Cu28-Ti(1-5) filler alloy.Hie joint of diamond and hard alloy formed under conditions that pressure was less than 5×10^-2 Pa,brazing temperature at 850 Tl and holding time of 10 min.The interface of the diamond film and the active filler metal was observed by scanning electron microscope-energy dispersive spectroscopy and X-ray to dislcose the bonding medanism mechanism.At the brazing temperature,there is greater affinity between active element(β-Ti) in the brazing filler metal and the carbon on the surface of the diamond film.A metal-like layer of TiC formed on the surface of diamond film due to adsorption,diffusion and chemical reaction.The layer and the Ag-Cu alloy based brazing filler metal bond the diamond film and the hard alloy together.Using the technical parameters,the four-point bending strength test shows that the average strength of the brazed joints is higher than 300MPa when the active element is less than 3%.