In the laser additive manufacturing process of superhard tools， diamonds are highly susceptible to the direct irradiation of laser beams and the influence of high-temperature melt pools， leading to phenomena such as graphitization and other thermal damage. A typical metal bonding agent CuSn10 powder for diamond abrasives is selected， and the Powder Bed Fusion-laser Beam （PBF-LB） technology is used to prepare CuSn10-diamond composites in this study. Focusing on two key factors affecting the performance of diamond particles in the manufacturing process， high-energy laser beams and high-temperature melt pools， individual diamond particles are selected as the research subject. A finite element simulation analysis is conducted to construct a temperature field model of diamond particles， reflecting the thermal evolution process of diamond particles in PBF-LB. The study elucidates the thermal damage mechanism of diamonds during the PBF-LB process， revealing that the graphitization transformation of diamonds is not caused by direct laser irradiation but is induced by the thermal effects of high-temperature melt pools. The critical temperature for graphitization of CuSn10-diamond composite material in the PBF-LB process is 1 491.6 °C. Furthermore， a quantitative relationship is established among the PBF-LB process-diamond particle temperature-degree of graphitization-frictional wear performance， demonstrating that with the increase of diamond particle temperature， the degree of graphitization increases， seriously damaging the friction and wear performance of the composite material.