<p>Existing studies have well investigated the spatiotemporal variations and environmental controls of land surface phenology (LSP); however, the combined effects of urbanization and topography on LSP remain poorly understood. Thus, we investigate LSP dynamics and their driving factors along urban–rural and topographic gradients in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), a region characterized by both rapid urbanization and topographic diversity, using space-borne 250&#xa0;m MOD13Q1 EVI, meteorological reanalysis products, and land cover data from 2000 to 2024. Our results show a prevalent trend of shortening of growing season, i.e. denoted by the length of season (LOS), across the study area over the investigated 25&#xa0;years, mainly due to the delay in the start of season (SOS) integrated with an advance in the end of season (EOS). The shortening trend of LOS was more pronounced in low-elevation and highly urbanized regions than other regions in the GBA. Mechanistic analysis reveals that spring thermal accumulation, quantified by growing degree days (GDD), is the primary determinant factor controlling the SOS timing across all zones, though its relationship is complex. Latitude is a primary controlling factor for EOS, yet its influence is modulated by local drivers that differ across the gradient. The hierarchy of secondary drivers for both SOS and EOS, however, showed a clear transition from anthropogenic thermal factors in urban cores to natural topographic factors in outlying areas. Furthermore, the interannual variation in EOS is the primary driver of LOS changes across almost all stable vegetated areas. This study underscores the necessity of considering both anthropogenic and natural environmental gradients, as well as their interactions, to accurately assess the responses of vegetation phenology to climate change in mega-urban regions.</p>