Abstract: Diamond has the advantages of high hardness, high thermal conductivity, and good chemical stability, and is widely used in the fields of superhard tools, semiconductors, optics, and electronic devices. However, the high interfacial energy between diamond and metals affects the performance of diamond/metal composites, and improving the interfacial properties has become the research hotspot. First-principles calculations can reveal the interfacial structure and properties of diamond/metal composites from the atomic and electronic scales. The theoretical basis of first-principles calculation method was expounded on this article, the applications of first-principles calculations in interfacial interactions, thermophysical properties, and mutual chemical interactions of diamond/metal composites were systematically reviewed, and the existing problems and future prospects were also discussed. It is found that the crystal plane, termination species, and element doping have the significant effects on the interfacial bonding and properties, and strengthening the interfacial bonding is beneficial for improving the thermal conductivity of the composites.