Abstract: In view of the poor machinability of diamond/copper composites, a split diamond/copper composite microchannel heat dissipation system is designed in this paper and compared with a pure copper microchannel system. The heat transfer characteristics of the two microchannel systems at different flow rates (0.3m/s, 0.5m/s, 0.7m/s) and rib heights (1mm, 1.5mm, 2mm) were investigated using HFE-7100 as the heat transfer medium. When the flow rate is 0.7 m/s, the chip surface temperatures of diamond/copper microchannels at the critical power are lower than those of pure copper microchannels by 12°C, 19°C, and 19.6°C, respectively, with the increase of rib height. The heat transfer coefficients were maximally enhanced by 27.8%, 30.1%, and 28.1% at the three rib heights, respectively, showing the heat dissipation advantages of the diamond/copper composite microchannels. The inlet and outlet pressure differences of the two microchannel systems are almost the same in the single-phase convection section, and the difference gradually arises when entering the nuclear state boiling, and the differential pressures of the diamond/copper microchannel systems are all slightly higher than those of the pure copper microchannel system at the critical power, with a maximum increase of 11.8%.