Abstract: Regenerative cooling serves as a vital thermal protection approach for high-speed flight propulsion systems. Quantitatively revealing the fluid-solid coupled heat transfer rules in cooling micro-channels is crucial for the design and optimization of regeneration cooling structures. In this paper, computational fluid dynamics (CFD) numerical simulation were conducted to systematically analyze the fluid-solid coupled heat transfer process of supercritical hydrocarbon fuel in microchannels. The effects of hydraulic diameter D, wall thickness u, cross-sectional shape, and other factors on parameters such as surface heat transfer coefficient h, structural thermal resistance R_c, and flow resistance pressure drop Δp were compared. Results indicate that, influenced by drastic thermophysical property variations of supercritical fluid, the heat transfer in regenerative cooling microchannels can be divided into the near-wall pseudo-boiling region, mainstream pseudo-boiling region, and fully developed turbulent heat transfer region. The surface heat transfer coefficient h reaches its peak in the fully developed turbulent stage. Reducing hydraulic diameter D enhances heat transfer but increases the flow resistance pressure drop Δp; when D decreases from 3 mm to 1.73 mm, the channel pressure drop Δp increases approximately eightfold. Decreasing wall thickness u or increasing rib thickness B reduces structural thermal resistance R_c and improves cooling effectiveness. For every 30% reduction in the u/D ratio, the average structural temperature decreases by about 1.7%. Comparing different channel configurations, rectangular channels with an aspect ratio AR = 1.5–2.0 and flow area S ≈ 6 mm² demonstrate significant advantages in enhancing heat transfer and reducing flow resistance.