Highlights What are the main findings? Ecological quality from 2000 to 2025 remained predominantly at a medium level but exhibited an overall declining trend, characterized by degradation exceeding improvement and pronounced spatial clustering. Elevation, air temperature, and surface radiation constitute the dominant terrain-thermal control mechanism, exhibiting significant nonlinear interactions and spatial heterogeneity. What are the implications of the main findings? Process-oriented index reconstruction substantially improves ecological assessment reliability in sparsely vegetated alpine-arid regions. The findings provide a robust scientific foundation and monitoring framework for the long-term protection of fragile alpine ecosystems and the strategic development of Qiangtang National Park.Highlights What are the main findings? Ecological quality from 2000 to 2025 remained predominantly at a medium level but exhibited an overall declining trend, characterized by degradation exceeding improvement and pronounced spatial clustering. Elevation, air temperature, and surface radiation constitute the dominant terrain-thermal control mechanism, exhibiting significant nonlinear interactions and spatial heterogeneity. What are the implications of the main findings? Process-oriented index reconstruction substantially improves ecological assessment reliability in sparsely vegetated alpine-arid regions. The findings provide a robust scientific foundation and monitoring framework for the long-term protection of fragile alpine ecosystems and the strategic development of Qiangtang National Park.Abstract The Northern Tibetan Plateau is among the most climate-sensitive alpine regions globally. To address the limited applicability of the traditional Remote Sensing Ecological Index (RSEI) in sparsely vegetated areas, this study developed a Soil-Adjusted Remote Sensing Ecological Index (SRSEI) tailored to cold and arid environments. The ecological quality of the Northern Tibetan Plateau from 2000 to 2025 was systematically evaluated and analyzed. The results indicate that: (1) The improved SRSEI achieved a first principal component (PC1) contribution of 72.76%, a significant enhancement over traditional models that effectively mitigates noise from soil backgrounds and anthropogenic features. (2) Between 2000 and 2025, ecological quality was predominantly moderate, following a characterized east-to-west declining spatial gradient. Overall mean SRSEI values fluctuated between 0.420 and 0.476, exhibiting a marginal downward trend. (3) Ecological degradation affected 50.17% of the region, with 26.14% facing risks of sustained decline. Conversely, 40.11% of the area displayed potential recovery trends, suggesting potential spatial divergence in future ecological trajectories. (4) Regional ecological dynamics are governed by a topographic-thermal compound driving mechanism. Elevation (DEM), temperature (TEMP), and surface shortwave radiation (SRAD) emerged as the dominant explanatory variables. Furthermore, dual-factor interactions exhibited significant enhancement effects, while the influence of anthropogenic factors was comparatively weak at the regional scale. These findings provide a scientific basis for the long-term monitoring of fragile alpine ecosystems and the strategic development of the Qiangtang National Park.