Abstract: Vacuum brazing diamond with large-grained alloy filler was conducted to control the amount of alloying powder filler and improve the uniformity of filler layer during brazing of diamond. A geometric model was established in this paper. The relation equations between diamond and large-grained alloys were built to reach the optimal brazing effect, and the practical solutions based on wetting angle of solder were obtained. According to the measured wetting angle of nickel-based alloys, the large-grained alloying filler in 50 mesh matched the diamond in 60 mesh. The results of vacuum brazing and heavy load grinding tests show that the large-grained nickel-based alloys melted completely with good fluidity, and the diamond in 60 mesh was well embedded with good climbing effect. The diamond was exposed 60% to 70% with clean surface and free of impurities. After heavy load grinding test, edge abrasion, local breaking and worn flat on the diamond were observed, which proves the feasibility of this proposed technology.