Abstract: The integrated development of the Yangtze River Delta has been elevated to a national strategy, shouldering the historical mission of solving cross-regional governance challenges and innovating regional coordinated development mechanisms. To address the problems of administrative fragmentation and institutional barriers in the development of urban agglomerations, the research on regional coordinated development was innovatively expanded from an economic dimension to a policy dimension. By employing a staggered DID and based on data from 2005 to 2023 of 41 cities in the Yangtze River Delta region, the impact of the integrated development of the Yangtze River Delta on the level of urban public services was verified from both theoretical and empirical perspectives. The research finds that the integrated development of the Yangtze River Delta has significantly enhanced the level of urban public services, and this conclusion remains valid after a series of robustness tests. The mechanism analysis reveals that breaking down the barriers to the flow of resource elements is the key path: the integrated development of the Yangtze River Delta has enabled the free flow of human resources, logistics, capital, information, and technology, which are essential for creating public service value, thereby injecting core momentum into urban public services. Heterogeneity analysis indicates that the impact of the integrated development of the Yangtze River Delta on the level of public services varies significantly among cities of different sizes, locations, and natures: the benefits of integration are particularly evident in small and medium-sized cities, the Zhejiang and Anhui regions, and non-contracting cities. Therefore, it is necessary to summarize and promote the advanced experience of the integrated development of the Yangtze River Delta, expand the policy effects of its integrated development; remove the “bottlenecks” hindering the free cross-regional flow of resource elements, and optimize the rational allocation of public service resources in urban agglomerations, and strengthen the “trickle-down effect” and “radiation effect” of large cities on small and medium-sized cities, to achieve high-quality integrated development of public services in urban agglomerations.