Abstract: Urbanization is essentially a systemic transformation from an agricultural society to an urban society, with land urbanization serving as its core manifestation. Since the 1990s, China has experienced rapid land urbanization, which has led to issues such as “ghost cities”, reduction of arable land, ecological deterioration, and other problems, threatening food security and people’s livelihoods. Changes in land use patterns and resource allocation efficiency have profound impacts on ecological environment quality. So Scientifically assessing the spatiotemporal repercussions of land urbanization on ecological environment quality is not only a theoretical necessity but also a practical requirement for fostering regional sustainability. Drawing upon empirical data from 284 prefecture-level and above cities in China, this study constructs a comprehensive evaluation framework to measure the trajectories of both land urbanization and EEQ. By employing bivariate spatial autocorrelation analysis and spatial Durbin models to systematically investigate the spatial dependence, direct impacts, and indirect spillover effects inherent in the urbanization-environment nexus. The results show that: (1) During the study period, land urbanization levels in China rose steadily. Both land urbanization and ecological quality indices demonstrate continuous improvement, exhibiting a distinct “core-periphery” hierarchical spatial structure. The ecological environment quality index increased from 0.661 to 0.792, with an average annual growth rate of 0.93%, mainly driven by the expansion of green spaces and enhanced environmental governance. (2) The spatial correlation between land urbanization and ecological environment quality exhibits four typical correlation patterns: “high-high synergy”, “high-low imbalance”, “low-high heterogeneity”, and “low-low lag”. The intensity of spatial correlation increases, and the distribution pattern gradually evolves from a scattered to a clustered configuration. This is manifested by the expansion of high-high synergy areas and low-low lag areas, along with the contraction of high-low imbalance areas and low-high heterogeneity areas, confirming that the positive promoting effect of land urbanization on ecological environment quality has been continuously strengthening in the spatial dimension. (3) Contrary to localized benefits in specific zones, the overall land urbanization continues to exert a significant inhibitory effect on local ecological environment quality. Furthermore, the SDM analysis confirms the existence of negative spatial spillover effects, indicating that GDP, IND, and TEC positively contribute to ecological quality, POP shows significant negative effects. And the environmental impacts demonstrate spatiotemporal heterogeneity: short-term negative effects outweigh long-term impacts temporally, while spatially, eastern regions exhibit positive effects contrasting with negative impacts in central-western and northeastern regions-disparities attributable to compounded factors including locational advantages, development models, ecological carrying capacity, and policy interventions. To harmonize urbanization and environmental health, these findings suggest implementing differentiated land-use policies, improving market-based allocation mechanisms, and strengthening institutional safeguards for ecological protection to guide sustainable urban land development. And the marginal contributions of this research are threefold: Theoretically, it integrates spatial spillover effects and spatial-temporal heterogeneity into a unified analytical framework, refining the theoretical system of urbanization-environment interactions. Methodologically, the use of the Spatial Durbin Model effectively addresses endogeneity and spatial dependence, while effect decomposition reveals the specific direct and indirect pathways of influence. Practically, the study provides empirical evidence and decision-making support for crafting differentiated regional sustainability policies, optimizing territorial spatial development, and improving ecological compensation mechanisms.