Can New Industrial Land-Use Policy Drive Urban Digital–Green Synergistic Transformation? Evidence from a Quasi-Natural Experiment in China

Against the backdrop of tightening construction land constraints compounded by the “dual carbon” goals, the quality of industrial space supply both constrains the expansion of digital industries and shapes the pace of green transformation. The new industrial land-use policy (NILUP) is an institutional reform that starts from the rules of industrial space supply. This study treats the staggered issuance of NILUP documents by cities in batches as a quasi-natural experiment. Based on panel data for prefecture-level cities from 2009 to 2024, it applies staggered difference-in-differences, event study, heterogeneity-robust estimation, double machine learning, and spatial econometric methods to identify the effect of NILUP on urban digital–green synergistic transformation (DGT), measured by a composite index built with the coupling coordination degree model. Under the identifying assumptions of parallel trends and no unobserved time-varying confounding, the results show that NILUP significantly raises urban DGT by 0.0122, and the coefficient remains positive after replacing the estimator, adjusting the sample, and changing how the index is constructed. The improvement comes from a joint rise in the levels of the digital and green subsystems rather than from closer coupling between them, as the coupling degree does not increase significantly. Furthermore, NILUP improves urban land-use efficiency and raises a gravity-based factor-attraction index, which is consistent with factor attraction but is not direct evidence of realized factor inflows. By city type, the promoting effect of NILUP is stronger in provincial capitals and sub-provincial cities, large-scale cities, and non-resource-based cities. On policy interaction, DGT improves more markedly when NILUP is implemented jointly with Broadband China and new-type urbanization, although the new-type urbanization interaction is identified from only 15 cities and is exploratory. Across the examined spatial specifications, there is no stable evidence of spillovers to the DGT of neighboring cities, and the local effect remains robust after controlling for spatial exposure. The findings indicate that restructuring industrial land supply rules can provide spatial support for urban digital–green synergistic transformation. Embedding green constraints simultaneously in industry entry and performance supervision could also be considered.