Abstract: In order to prepare diamond/copper composite materials with good thermal and physical properties, the surface of diamond particles was modified by chromium plating, and the composites were prepared by vacuum hot pressed sintering(VHP). The thermal conductivity, thermal expansion coefficient, and bending performance of the composites were tested, and the optimum process parameters of the composites prepared by VHP method were studied. The results show that chromium plating on the surface of diamond can improve the interface bonding of the composites. The flexural strength of the composites increases with the increase of sintering temperature, and the flexural strength of the composite material prepared at 1 100 ℃ reaches 278 MPa. When the other conditions are the same, the thermal conductivity of the composite is 417 W?m-1?K-1 when the thickness of the chromium layer on the diamond surface is 150 nm, while the thermal conductivity of the composite without chromium plating is only 127 W?m-1?K-1. As the sintering temperature increases, the thermal conductivity of the composites increases. When the sintering temperature is 1 050 ℃ and the pressure is 20 MPa, the thermal conductivity of the chromium-plated diamond/copper composite can reach 574 W?m-1?K-1. In the range of 25~300 ℃, the thermal expansion coefficient is between (3.50~8.50) ×10-6 K-1, and increases with the increase of ambient temperature.