Abstract: In this study, taking the Yuan Shangdu site as an example, the hydrothermal coupling driving mechanism of root-layer separation disease evolution under the combined action of snow cover, freeze-thaw and vegetation roots is revealed. Multi-point hydrothermal sensors and time-lapse photography are deployed inside and outside the experimental wall to capture the seasonal temperature disturbance and water migration of the root layer and the lower rammed soil. The results show that freeze-thaw disturbance is concentrated in the top 0-40 cm beneath the wall surface, with the 0-30 cm sublayer being particularly active: frequent crossings of 0℃ yield more than 80 freeze-thaw cycles per year, inducing structural fatigue and particle loosening in the active layer. In contrast, a water-rich, refreezing-induced shear-weakening band develops at 30-40 cm, acting as a potential slip surface. In the spring snowmelt period, the chain process of "sunny thawing, shade enrichment, and interface weakening" constitutes a typical "hydrothermal coupling" synergistic failure mechanism. The research constructs a framework for root layer separation disease mechanism and hydrothermal synergy, which provides theoretical support and engineering application basis for dynamic disease monitoring and precise intervention of similar earthen heritage sites.