<p>Freeze–thaw erosion is a prevalent surface process in cold regions, driven by the cyclic freezing and thawing of soil and rock. This process results in land degradation, soil erosion, and a range of ecological and environmental challenges, posing significant threats to the ecological security and socio-economic development of high-altitude mountainous areas. This study focuses on the high-cold mountainous regions of northwestern Yunnan, employing multi-source remote sensing data and geographic information system (GIS) technologies. Eight key evaluation factors were considered, including annual freeze–thaw cycle duration, daily average phase-change water volume, annual precipitation, slope, aspect, vegetation coverage, soil type, and soil erodibility. By integrating expert scoring with principal component analysis, a comprehensive system was developed to identify and assess the intensity of freeze–thaw erosion zones in the region. The spatiotemporal evolution of freeze–thaw erosion intensity from 2017 to 2023 was systematically analyzed. The findings suggest that high-altitude regions face considerably greater erosion intensity, attributed to lower temperatures and frequent freeze–thaw cycles. In contrast, low-altitude areas are comparatively less affected. This reflects the intricate interplay of climatic and environmental dynamics. Over the 7-year period, areas of mild and moderate erosion expanded significantly, whereas regions of minimal and intense erosion showed a decline. Annual precipitation and freeze–thaw cycle duration emerged as the primary factors influencing the spatial distribution of erosion intensity. This study offers valuable insights and decision-making support for ecological conservation and disaster mitigation in the high-cold mountainous areas of northwestern Yunnan.</p>