Abstract: Diamond has advantages of high hardness, high thermal conductivity, and good chemical stability, and is widely used in fields such as superhard tools, semiconductors, optics, and electronic devices. However, the high interfacial energy between diamond and metal affects the performance of diamond/metal composites. Improving its interfacial properties has become a research hotspot. First - principles calculations can reveal the interfacial structure and properties of diamond/metal composites from the atomic and electronic scales. This article expounds on the theoretical basis of the first - principles calculation method and systematically reviews its applications in the research of interfacial interactions, thermophysical properties, and mutual chemical interactions of diamond/metal composites. It is found that different crystal planes, termination species, and element doping have significant effects on the interfacial bonding and properties, and strengthening the interfacial bonding is beneficial for improving the thermal conductivity of the composites. The article also analyzes the existing problems in current research and looks forward to the future development directions, providing theoretical support for promoting the research and application of diamond tools and their composites.