Global warming has intensified freeze-thaw activity in high-latitude and high-altitude regions; along the western sector of the farming-pastoral ecotone in northern China, pronounced seasonal freeze-thaw cycles now pose a severe threat to land resources. This study aims to quantitatively reveal the spatial differentiation patterns of freeze-thaw erosion in the western segment and its influencing factors. This study begins with the fundamental concepts of freeze-thaw erosion, grounded in soil mechanical fragmentation and gravitational migration. Critical slope is used as the identification criterion to delineate freeze-thaw erosion zones. Building upon this foundation, a Random Forest model is employed to calculate the weighting factors influencing freeze-thaw erosion in the western segment of the northern agro-pastoral transition zone, thereby constructing a graded evaluation model for freeze-thaw erosion intensity. Results indicate the following: (1) Freeze-thaw erosion exhibits no discernible distribution pattern in the western segment, appearing scattered, while non-freeze-thaw erosion is primarily concentrated in the northern region. (2) Freeze-thaw erosion intensity ranges from 1.48 to 4.58 in the western segment. The total area of the study region is 151,000 km2, the affected area spans 122,400 km2, accounting for 81.11% of the total regional area. (3) Regionally, the Hehuang Valley exhibits predominantly strong and severe erosion, while the northern Loess Plateau shows mostly slight erosion. The southern Loess Plateau features light and moderate erosion with scattered instances of severe erosion. (4) Vegetation coverage and soil moisture are the primary contributing factors to freeze-thaw erosion. This study proposes, for the first time, a method that couples annual freeze-thaw day cycles with a critical slope threshold to delineate freeze-thaw erosion zones, demonstrating broad applicability. It systematically uncovers the spatial heterogeneity of freeze-thaw erosion in the western sector, substantially advancing scientific understanding of the process and providing a theoretical basis for its targeted management.