As the integrated regional development of the Yangtze River Delta has become a national strategy of China, the scope of regional integration has expanded and regional economic geography has changed, which has a profound impact on regional environmental governance. Based on the 3D analysis framework of new economic geography, this paper used the 3D analysis framework of new economic geography to study the impact of regional market segmentation, density, distance, and other economic and geographical factors on urban environmental governance in the Yangtze River Delta. Based on the panel data of 41 cities in the Yangtze River Delta from 2003 to 2019, this paper used the relative price method to calculate the market segmentation index of the cities in the delta, built a comprehensive evaluation index system for environmental governance, and used the global entropy weight method to measure the urban environmental governance index. The empirical research mainly drew the following conclusions: ① The level of urban environmental governance in the Yangtze River Delta was on the rise, and there were obvious regional differences in environmental governance. These regional differences mainly came from the gap between provincial administrative regions, but the regional gap showed a trend of convergence as a whole. ② Judging from the impact of economic and geographical factors on urban environmental governance in the Yangtze River Delta, market segmentation had a significant negative impact on urban environmental governance. After using instrumental variables to alleviate endogenous biases, market segmentation had a greater negative effect on urban environmental governance. The relationship between environmental governance and economic density, as well as between environmental governance quality and population density, showed an inverted U-shaped relationship. The improvement of traffic accessibility was conducive to improving urban environmental governance. The geographical distance from the regional central city had a significant negative impact on urban environmental governance. Robustness tests were carried out from different perspectives, and the above research conclusions still held. ③ Environmental governance had positive spatial autocorrelation. The spatial spillover effect of economic geographical factors such as market segmentation, economic density, and population density on the environmental governance of surrounding cities was just opposite to its impact on local environmental governance. Therefore, it is necessary to speed up the unified large market construction and market integration in the Yangtze River Delta, enhance the accessibility of transportation between cities in the delta, control the economic density and population density of cities, prevent environmental governance risks caused by excessive economic density and population density, build a long-term synergistic mechanism, and promote the coordinated improvement of urban environmental governance in the delta. [ABSTRACT FROM AUTHOR]