The relationship between urban ecological environment and urbanization is a key to sustainable urban development. Studying the long-term evolutionary trends of vegetation cover under different levels of urbanization is important for understanding the effects of urbanization processes on vegetation growth dynamics, urban regeneration, and advancing scientific management of urban greening. However, the understanding of the differences in vegetation growth trends along urban-rural gradients within cities was still relatively limited. Based on the MODIS-NDVI data of the Yangtze River Delta (YRD) from 2000 to 2020, this study investigated the urban-rural differences in vegetation cover evolution within the cities of the YRD using trend analysis and geographic probe methods, and analyzed the causes from the perspectives of land use/cover change and urbanization development. The results showed that (1) the vegetation in the Yangtze River Delta region showed a greening trend in general from 2000 to 2020, with the largest proportion (52.06%) of vegetation being significantly green, 31.68% being slightly green and stable unchanged areas, and 6.82% being sporadically distributed in browning areas. (2) The change of vegetation cover in the old urban areas of the region showed a general trend of returning to green (0.016/10 a), browning in the new urban areas was obvious (-0.019/10 a), and greening in the agricultural suburban areas was prominent (0.023/10 a). In cities with a high level of population urbanization, such as Shanghai, Nanjing and Hangzhou, the old urban areas with the highest intensity of land use change also had the highest greening trend, reflecting the promotion of green space by the urban renewal process; while in cities with a relatively low level of population urbanization, such as Xuancheng, Bengbu and Fuyang, the agricultural suburban areas with a relatively low intensity of land use change also showed an obvious greening trend, more influenced by regional ecological protection. (3) Land urbanization was the dominant factor of vegetation cover change in old and new urban areas in the Yangtze River Delta, while the urbanization factor was generally insignificant in explaining the degree of suburban areas. From the overall region of the Yangtze River Delta, three factors, namely the proportion of urban population, impervious area/total area and gross regional product, had significant effects on the evolution of vegetation cover, among which the proportion of urban population has the greatest influence.