The poor wettability between diamond and copper greatly affects the thermal conductivity of composite materials. To improve diamond-copper wettability and strengthen interfacial bonding, tungsten (W) was deposited onto diamond surface by a molten salt method to achieve the surface metallization of diamond, and the influences of molten salt plating temperature and holding time on the diamond coating were investigated. Subsequently, W-coated diamond particles were consolidated into Cu matrix composites by spark plasma sintering (SPS), and the correlations between molten salt coating parameters and the thermal conductivity of diamond/Cu composites were systematically explored. The results indicated that high plating temperature and appropriate holding time were beneficial for the formation of high-quality tungsten carbide coatings on diamond surfaces. At a coating temperature of 1000℃ and a holding time of 90 min, diamond reacted with tungsten powder to form a uniform, intact and nearly defect-free tungsten carbide (WC) coating. The formed coating enhanced the interface bonding between diamond particles and copper matrix, thereby effectively improving the thermal conductivity of diamond/Cu composites. The prepared diamond/Cu composite achieved a maximum thermal diffusion of 208.77 mm2/s and a peak thermal conductivity of 579.52 W/(m?K). Plating temperature and holding time of diamond had a significant impact on the thermal conductivity of composite materials. Optimizing these two parameters enabled the construction of a thin, continuous, stress-matched and low thermal resistance interfacial layer, maximizing the thermal conductivity of diamond/Cu composites. This work provides a theoretical basis for optimizing the thermal conductivity of diamond/Cu composites and the selection of the interface carbide layer.