Taking the brazed diamond bit as research object, the paper analyzes and summarizes the thermal dynamic theory of the heating process in high temperature brazing furnace and the cooling molding process, and makes the numerical simulation for the cooling process on the whole entity model after being removed from the brazing furnace. By analyzing the temperature field of brazed diamond bit and cooling molding process as well as the effect of the temperature field on the stress field of brazed diamond bit, the stress between the inner graphite mold and the brazed diamond bit was also analyzed. The comparison was made on the simulation data with theoretical calculated values, which verified the good consistency between the numerical simulation and theoretical value of brazed diamond bit’s cooling process.