<p>Cu/diamond composites, as a new generation of thermal management materials, integrate stable chemical properties with exceptional thermal conductivity and mechanical performance, making them a central focus of current research. However, interfacial issues between diamond and Cu, including poor wettability, significant acoustic mismatch, and the absence of direct chemical bonding, lead to insufficient interfacial bonding and the formation of void defects. This constitutes a critical technical challenge that constrains further enhancement of thermal conductivity. This paper summarizes the fundamental mechanisms of key manufacturing processes, including high-temperature high-pressure (HTHP) sintering, vacuum hot-pressing sintering (VHPS), and spark plasma sintering (SPS). It further explicates the core principles of thermal-conductivity prediction models such as the Hasselman-Johnson (H-J) model and Differential Effective Medium (DEM) model, along with their quantitative descriptions of interfacial thermal resistance. Key factors affecting the thermal conductivity of these composites are systematically reviewed, encompassing diamond particle size, volume fraction, surface microstructure, and interfacial modification strategies. The paper also examines recent progress in interfacial modification techniques, particularly the engineered formation of dense and continuous carbide transition layers through matrix alloying or diamond surface metallization. Finally, recommendations for future research include precise control and multiscale structural design of interfacial transition layers, innovations in low-temperature and low-damage fabrication processes, and closer integration of computational simulations with experimental validation. Through a comprehensive synthesis of theoretical and experimental insights, this study provides essential guidance for interface optimization and improved thermal management performance in Cu/diamond composites.</p>