Abstract: With the development of electronic devices towards miniaturization, high computing power and high integration, the power density within spaceborne high-performance computers has increased dramatically. Consequently, it’ difficult for traditional structural configurations and conventional materials to meet the heat dissipation requirements under escalating power. A high-performance spaceborne computer with low-thermal-resistance stacked architecture is designed, with the heat dissipation cold plates in critical high-density and high-power board modules adopting high-conductivity graphite-aluminum “sandwich” composites. Numerical simulations are employed to find the effects of conventional aluminum alloy cold plates and graphite-aluminum composite cold plates on the heat dissipation capabilities of both the key board modules and the computer system. Results show that the graphite-aluminum composite cold plates reduce the maximum temperatures of high-power CPU-memory board modules and power board modules by 10 ℃ and 4.0 ℃ respectively, with weight reductions of 11 g and 26 g respectively. And the greater the power consumption of the device is, the more pronounced the enhanced cooling performance of the graphite-aluminum composites becomes. The experiment result shows that the simulation errors are within ±10%, which confirms the accuracy and feasibility of the numerical simulation model.