<p>Vegetation is crucial for ecosystem health and socio-economic sustainability, especially in densely populated areas. However, its variation is complex due to natural and anthropogenic influences. This study examines vegetation greenness in China's eastern coastal region (ECR), the most developed region in China, using the Normalized Difference Vegetation Index (NDVI) from 1990 to 2019. The Geodetector method was employed to quantify the impacts of 12 indicators associated with natural and anthropogenic factors on vegetation greenness. Results show that the ECR exhibited poor to moderate vegetation greenness throughout the study period, with significant spatial differentiation. The region experienced vegetation browning from 1990 to 2000, followed by greening from 2000 to 2019. According to the <i>q</i> value of factors calculated by Geodetector, natural factors including annual mean temperature, annual total precipitation, and soil type dominated the spatial differentiations of vegetation greenness, with the interaction between precipitation and soil type being particularly significant. However, the influence of these natural factors weakened over time, while anthropogenic and topographic factors gained importance. Notably, the explanatory power of land use type for the spatial differentiation of vegetation greenness increased sharply between 2015 and 2019, likely due to landscape fragmentation caused by rapid urbanization. Two-factor interactions further confirmed the growing role of anthropogenic factors. The study underscores the importance of considering temporal changes in the roles of different factors in vegetation dynamics.</p>