How does the high-speed rail network reinforce the dominance of core cities in regional China?

Over the past two decades, the rapid expansion of China’s high-speed rail (HSR) network has significantly enhanced regional accessibility and connectivity. This paper investigates how the HSR network reshapes regional spatial structures and consolidates the dominance of core cities, using the Central Plains urban agglomeration (CPUA) in China as a case study. Based on train timetables and intracity transport data from 2010 to 2021, this study employs door-to-door travel time to measure HSR accessibility and weighted degree centrality (WDC) to examine HSR connectivity. Results reveal that the overall average travel time across the CPUA declined by 35.02%, while Zhengzhou’s average travel time declined by 20.93%, accompanied by substantial expansions in its 2 h and 3 h HSR travel radii. Zhengzhou’s WDC surged by 1600.98%, far outpacing the regional average growth of 858.32%, and the coefficient of variation rose from 64.43% to 93.08%, confirming a pronounced polarisation effect. Institutional prioritisation of the HSR development pattern, encompassing planning guidance, infrastructure construction and service distribution, has collectively enhanced a core–periphery spatial structure within the CPUA. This study improves the understanding of the relational dynamics between HSR network development and spatial restructuring, with broader implications for HSR planning and regional development policy.