Abstract: To address the bottleneck in thermal dissipation capacity of traditional aluminum alloy heat sinks, this study investigates a sandwich-structured graphite-aluminum composite. Comparative experiments demonstrate its superior lateral heat dissipation over aluminum alloys. A semi-physical calibration method was employed to quantify both in-plane 390 W/(m·K) and through-plane thermal conductivities of the graphite layer and composite. The results reveal that the graphite-aluminum composite achieves copper-equivalent heat dissipation 390 W/(m·K) in-plane with significantly lower density, demonstrating substantial advantages for aerospace lightweight engineering. The quantified thermal parameters enable thermal designers to efficiently develop optimized solutions through simulation-driven design iterations.