Urban land development intensity is a comprehensive reflection of the present situation of land use and the starting point of sustainable utilization in the future. It is also a comprehensive index reflecting the breadth of urban land development and carrying capacity of population and social and economic development. Based on the remote sensing monitoring data of land use in the Yangtze River Delta from 2000 to 2015, this study examined the spatiotemporal differentiation and influencing mechanism of urban land development intensity by using spatial analysis, multiple regression, and spatial error regression models, in order to improve land use efficiency and environmental quality. The main conclusions are as follows: (1) The index value of urban land development intensity in the Yangtze River Delta had been increasing from 0.089 in 2000 to 0.165 in 2015, which is higher than the national average of 0.046 in the same period. The development intensity of the “Z” axis of the Nanjing-Shanghai-Hangzhou-Ningbo area is higher than the regional average, which is consistent with the level of social and economic development. The development intensity of surrounding counties and cities is relatively low, and the spatial structure of core-periphery is remarkable. (2) Urban land development intensity shows a positive spatial correlation. Urban construction and industrial development are based on trunk transportation network and core urban areas. Economic spillover and foreign capital injection make the export-oriented economic development of surrounding counties very distinctive. The heterogeneity of land development intensity is high and relatively stable, and the spatial layout gradually reaches equilibrium step by step. However, the correlation gradually weakened in time. (3) The constraints of natural conditions on urban land development are weakening, and the deep industrialization and transformation and upgrading of industrial structure lead to efficient urban construction land development. Urbanization gathers a large number of immigrants, and the construction of highly developed transportation network facilitates the inflow of talent, capital, technology, and other essential resources. Both the level of social development and the force of economic development have become important factors that promote the enhancement of regional land development intensity. Meanwhile, the spatial agglomeration effect of higher urban administrative level in infrastructure investment, talent attraction, transportation facilities, and other aspects also promotes the large-scale development of urban land.