<p>Under the background of negative population growth in China, the construction of infrastructure can effectively promote population mobility and reallocation. As the core of the national large-scale clean energy infrastructure, the West-East Gas Pipeline (WEP) facilitates the efficient cross-regional allocation of energy resources and drives urban green development. However, does it also affect population mobility in shrinking cities? By using urban data from 2006 to 2023, this study analyzes the impact of WEP II on population mobility in shrinking cities along its route. The results indicate that the WEP II significantly reduces population outflow from shrinking cities along its route. The internal mechanism is explained by the improvement of wage, urbanization and urban green development performance brought by WEP II. Heterogeneity analysis shows that WEP II had a significant inhibitory effect on population outflow from shrinking cities of Eastern China, Central China, and non-resource-based, while the influence is not significant in Western and Northeastern China. Shrinking cities exhibit a “serious shrinkage in north, slight shrinkage in the south” pattern, spatial analysis confirms a “north-south” gradient in urban shrinkage intensity. Spatial econometric analysis further reveals that the WEP II has significantly inhibited population outflow from shrinking cities along the pipeline, while promoting population outflow from geographically adjacent shrinking cities. This study provides empirical evidence on the impact of energy infrastructure on regional population mobility and offers an important theoretical basis and practical reference for advancing the energy revolution, improving regional coordinated development strategies, and constructing sustainable urban development models.</p>