National-level urban agglomerations represent a crucial spatial strategy tasked with the dual missions of fostering regional development and advancing national modernization. Whether this strategy can effectively stimulate consumption growth is a critical issue demanding empirical investigation. Utilizing panel data from 256 prefecture-level and above cities in China spanning 2010-2023, this study employs both staggered Difference-in-Differences (DID) and Propensity Score Matching Difference-in-Differences (PSM-DID) methodologies to empirically examine the impact of the national-level urban agglomeration policy on resident consumption rates and its underlying mechanisms. The findings indicate that the policy significantly increased the resident consumption rate in the designated cities by approximately 1.51%. This conclusion remains robust across a series of validation checks. Mechanism analysis reveals that the policy effect is positively transmitted to resident consumption primarily through a significant reduction in central city primacy. This reduction, in turn, facilitates improvements in intra-regional income distribution, promotes the popularization of digital financial services, and encourages the diffusion of digital consumption platforms. Further heterogeneity analysis suggests that the policy’s effectiveness is significantly contingent upon the cities’ geographical morphology and industrial structure characteristics. Conversely, its association with human capital levels and subway accessibility appears limited. These research conclusions offer significant insights for achieving synergy between the objectives of boosting domestic demand and advancing spatial development during China’s upcoming “15th Five-Year Plan” period.