Analyzing the spatiotemporal characteristics and driving mechanisms of the coupling coordination between the green transition of urban land use (GTULU) and urban land use efficiency (ULUE) can help explore the future development direction of sustainable land use in cities. In this paper, we construct a theoretical framework for the coupling coordination between GTULU and ULUE. We use several models, including the super-efficiency slack-based model (SBM), the coupling coordination degree model, the non-parametric kernel density estimation method, exploratory spatial data analysis, and the geographically and temporally weighted regression (GTWR) model to examine the real level of GTULU and ULUE in the Yangtze River Delta region (YRDR) from 2003 to 2020. Based on this, we investigate the spatiotemporal evolution characteristics and driving mechanisms of the two coupling coordination processes. The study found that: (1) from 2003 to 2020, the overall trend of the coupling coordination between GTULU and ULUE in the YRDR tended to be coordinated and developed, but still at a primary coordination level, with sufficient room for improvement in the future. (2) The coupling coordination level of each city in the YRDR from 2003 to 2020 showed obvious spatial non-equilibrium and correlation characteristics, initially exhibiting convergent growth and later showing polarization effects; the spatial pattern of high-value areas showed a regularity of prioritizing Shanghai and Zhejiang Province, gradually penetrating into Jiangsu Province and Anhui Province. (3) Economic and social factors positively impacted the coupling coordination degree. Natural factors had a mainly positive impact in the southern and northern regions and a mainly negative impact in the central and eastern regions. The impact of natural factors has undergone a transition from a mainly positive impact to a mainly negative impact. Research conclusions include establishing a regional collaborative development mechanism, utilizing the spatial spillover effect of leading cities; optimizing industrial structure, improving infrastructure, and increasing research investment further to expand the driving effects of economic and social factors; and optimizing the layout of urban and rural construction land, enhancing the connectivity and uniformity of land parcels, and suppressing the negative effects caused by natural factors.