Understanding the thermal stability of soil organic carbon (SOC) facilitates interpreting soil responses to environmental factors, comprehending SOC stability, and its thermal dynamic characteristics, thereby revealing the impact of environmental elements on the carbon cycle. This study focuses on soils at various altitudes on the western slope of Helan Mountain, analyzing soil physicochemical properties, base cations, thermogravimetric (TG) curve characteristics, thermal stability parameters, and drivers of thermal stability. The results indicate that, with increasing altitude, soil physicochemical properties generally show an increasing trend, except for bulk density (BD), pH, and available phosphorus (AP); base cations are mainly concentrated in lower altitude areas; the mass loss rate reflected by the TG curves increases; derivative thermogravimetry (DTG) curves exhibit a bimodal trend at mid and low altitudes and a unimodal trend at high altitudes; the temperature at which SOC mass is halved (TG-T₅₀) is relatively higher at mid and low altitudes; with increasing altitude, the ratio of SOC decomposition at lower temperatures to total SOC decomposition (Exo₁/Exo_t) gradually increases, while the ratio at higher temperatures (Exo₂/Exo_t) decreases, indicating higher thermal stability of SOC in soils at lower altitudes on the western slope of Helan Mountain; the correlation between physicochemical properties and SOC thermal stability is significantly stronger; soil organic matter (SOM) is the dominant factor affecting SOC thermal stability. In summary, SOC thermal stability on the western slope of Helan Mountain decreases with increasing altitude, with lower altitude soils containing more heat-resistant components and being relatively more stable.