Abstract: In view of the common root layer separation diseases in soil sites in sub-humid cold areas, this study took the Yuanshangdu site in Inner Mongolia as a typical object, and systematically revealed the hydrothermal coupling driving mechanism of disease evolution under the joint action of snow cover, freeze-thaw cycle and vegetation roots. In this study, multi-point temperature and humidity sensors and time-lapse photography equipment were installed inside and outside the experimental wall to capture the temperature disturbance and water migration process of the root layer in different seasons. The results show that the range of 0-40 cm is the main active zone of freeze-thaw disturbance, the top 0-30 cm is prone to high-frequency freeze-thaw fatigue and structural looseness, and the bottom 30-40 cm is the shear weakening zone due to water-rich freezing, which is a potential slip surface of root layer slip. Further analysis reveals that the spring snowmelt period constitutes a typical "heat-water-force" synergistic failure mechanism in the chain process of "sunny thawing-shady enrichment-interface weakening". The evolution model of root layer separation and disease potential identification method constructed in this study provide theoretical support and engineering practice basis for dynamic disease monitoring and precise intervention of similar soil sites.