Abstract: To reveal the spatiotemporal characteristics and driving mechanisms of eco-environmental quality in Beijing, we constructed the Remote Sensing Ecological Index (RSEI) based on Landsat TM/OLI imagery acquired in 2000, 2010, and 2020. We further employed principal component analysis (PCA) and the GeoDetector model to analyze the spatiotemporal variations in eco-environmental quality across different urbanization levels. Ecological factors including land surface temperature (LST), normalized difference vegetation index (NDVI), wetness index, and dryness index were selected to quantitatively evaluate their contributions to changes in eco-environmental quality, and to explore the combined effects of natural and anthropogenic drivers. The results showed that the mean RSEI in Beijing increased from 0.62 to 0.71 during 2000–2020, indicating a continuous improvement in eco-environmental quality. The RSEI values of the central urban area, suburban built-up areas, and remote mountainous areas increased from 0.35, 0.44, and 0.64 to 0.46, 0.55, and 0.73, respectively. Land surface temperature and socioeconomic factors exhibited relatively high explanatory power for changes in eco-environmental quality and showed enhanced interactions with other factors, revealing a differentiation mechanism dominated by the thermal environment and jointly driven by natural factors and human activities.