Abstract: This study investigates how thin plies affect moisture-aging coupling in carbon fiber reinforced polymer (CFRP) laminates and their impact on damage resistance and residual compression under hot-wet conditions. Three lay-ups—thick-ply, thin-ply and hybrid—were prepared and aged for 0, 20, 40 and 60 days. Moisture uptake and chemical degradation were measured by FT-IR and SEM. Drop-weight impact plus ultrasonic C-scan mapped damage growth, while digital image correlation (DIC) tracked the full compression-after-impact process. Thin-ply laminates absorbed the least water (~16% less than thick plies) because their dense interfaces slowed diffusion. After 60 days of hygrothermal aging, the reduction in residual compressive strength of the thin-ply laminates is only 8.3%, which is significantly better than that of the thick-ply laminates (23.6%) and the hybrid-ply laminates (14.3%). The improved interface and damage-suppression features of thin plies thus enhance damage tolerance in hot-wet service, providing experimental support for the design and safety assessment of composites under hygrothermal loads.