While the role of aeolian sand deposition in permafrost degradation has received substantial attention, much less is known about how it influences seasonally frozen ground. In particular, the mechanisms by which aeolian sand affects seasonally frozen ground remain poorly understood. To clarify how aeolian sand regulates the thermal regime, maximum seasonal freezing depth (MSFD), and freeze-thaw processes of seasonally frozen ground on the Qinghai-Tibet Plateau, we conducted continuous observations of the soil thermal regime under different aeolian sand-layer thicknesses in the Beiluhe River (BLH) and Honglianghe River (HLH) basins. We further quantified the relative contributions of climatic factors and surface conditions to variations in seasonally frozen ground. Our results show that aeolian sand cover significantly altered the soil thermal regime and MSFD. With increasing sand thickness (ST), the freezing period shortened (23.5% in HLH and 35.5% in BLH), the top-down thawing period was greatly reduced (to 11.4 +/- 5.7 d under thick sand in HLH and nearly absent in BLH), whereas the bottom-up thawing period was prolonged. Thick sand layers enhanced the freeze-thaw asymmetry, characterized by accelerated upper-layer freezing/thawing and slowed lower-layer processes. MSFD generally became shallower with increasing ST (similar to-0.3 cm & centerdot;cm(-1)). Feature-importance analysis based on XGBoost-SHAP indicates that air temperature is the dominant predictor of MSFD, whereas the direct contributions of precipitation and net solar radiation are weaker; however, thick sand layers combined with sparse vegetation (vegetation cover, VC < 30%) tend to increase MSFD. Partial least squares path modeling (PLS-PM) indicates that climatic forcing and local surface conditions jointly regulate freeze-thaw processes mainly through ground temperature responses, in which regional climate constrains the overall MSFD level, while ST and VC mainly modulate the local spatial pattern of MSFD. These findings provide a quantitative basis for thermal-insulation design and ecological restoration in engineering corridors across cold, aeolian-sand-affected regions.