Abstract: A high heat-conducting diamond/aluminum composite material with thermal conductivity of 677 W/(m·K) was prepared by vacuum hot-pressing solid-phase sintering. The properties of the diamond/aluminum composite were characterized by laser thermal conductivity instrument and thermal expansion instrument. The preparation process was optimized by modifying the preparation temperature, holding time and diamond particle size. It was noted that the density and relative density of diamond/aluminum composite increased with the increase of the preparation temperature, and the thermal conductivity first rose and then fell. When the preparation temperature was 650 ℃, the thermal conductivity reached 526.2 W/(m·K). When the heat preservation time increased from 30 minutes to 120 minutes, the density, the relative density and the thermal conductivity of diamond/aluminum composite materials all increased to the density of 99.1% and the thermal conductivity of 566.7 W/(m·K). When the size of diamond particle increased from 20 μm to 500 μm, the density and relative density of diamond/aluminum composite first increased and then decreased. When the size of diamond particle is 200 μm, the density and relative density reached their maximum values, namely 3.06 g/cm³ and 98.4%. The thermal conductivity increased with the increase of diamond size, and the thermal conductivity reached the highest 677.5 W/(m·K) when using 500 μm diamond particles as thermal conductive fillers. Therefore, high-density diamond/aluminum composite material prepared by vacuum hot pressing method can effectively improve the combination of aluminum matrix and diamond through process control, reduce interfacial void, and then prepare high thermal conductivity diamond/aluminum composite material.