<p>Elevation-dependent warming has been documented across major mountain ranges worldwide. Vegetation phenology serves as a sensitive indicator of ecosystem responses to climate change, and related metrics can reveal changes in vegetation productivity and in the global carbon budget. However, existing studies have mostly focused on the elevation dependence of climate change, whereas the characteristics and mechanisms of elevation-dependent changes in vegetation phenology remain poorly understood. The Tibetan Plateau, the worlds’ highest plateau, is an ideal region for investigating the relationship between phenological changes and elevation. This study selected Gaoligong Mountain on the southeastern margin of the Tibetan Plateau as the study area and used high spatiotemporal resolution remote sensing data to examine the elevation dependence of vegetation phenology and its response to climate change. The results indicated a significant “Z”-shaped nonlinear relationship between vegetation phenology and elevation, with critical thresholds at 2600 and 3600 m. Temperature had the largest effect on phenology below 2600 m, temperature and water availability were dominant factors at 2600–3600 m, and minimum temperature was dominant above 3600 m. These findings indicate that temperature was the primary factor affecting the elevation dependence of phenology, whereas precipitation and solar radiation had modulating effects that varied across elevation belts. The coupled relationships among topography, climate, and vegetation on the southeastern margin of the Tibetan Plateau improve understanding of phenological responses in complex mountain ecosystems.</p>