Cu-Sn-Ti brazing alloys are gaining importance as active brazing alloys for brazing diamond tools. The microstructure at the interface between diamond or Ti-coated diamond grits and Cu-Sn-Ti brazing alloy and bonding strength have been investigated in this paper. The results show that TiC layer forms between diamond and alloy matrix during the brazing process and Sn- and Ti-based intermetallic phase forms between TiC and the bonding matrix. And compound SnTi3 forms between the Ti-coated diamond grits and Cu-Sn-Ti brazing alloy. Furthermore, the bonding strength between Ti-coated diamond grits and brazing alloy is higher than that between diamond grits and brazing alloy.