Tungsten was plated on the surface of diamond by using thermal diffusion method. Different process parameters were employed to prepare the composites with tungsten, diamond and copper. The micro morphology of different samples was observed, and the thermal conductivity of samples was measured by laser flash method. The optimal process parameters for preparing diamond/copper composites with high thermal conductivity were investigated. The results indicated that plating tungsten on diamond could modify the interface bonding. When the diamond was plated for 60 min, the coating appeared intact, uniform and flat, and the thermal conductivity of the sample could reach as high as 486 W/(m·K). The integrity and uniformity were more important than thickness for the coating. When the tungsten-plated diamond was further annealed, the metallurgical bonding between the coating and the diamond was enhanced, and the thermal conductivity rose to 559 W/(m·K).