<p>As critical transportation infrastructure, railways exert a profound influence on regional economic development. However, existing studies mostly adopt global regression models and treat railway openings as dummy variables to compare the effects before and after their operation. Research that employs smaller spatial units and conducts spatial-temporal heterogeneity analyses across multiple periods on the basis of actual changes in accessibility remains limited. Using actual train timetables, this study examines railway-driven accessibility changes in Fujian, China, across four representative years. To investigate the link between railway expansion and regional economic development disparities, we apply a Multiscale Geographically and Temporally Weighted Regression (MGTWR) model. The model accounts for multiscale effects through variable-specific spatial and temporal bandwidths. Consequently, it offers nuanced insights into the evolving relationship between railway expansion and regional disparities in economic development. Railway expansion was accompanied by substantial improvements in accessibility and accessibility equity across counties in Fujian. The launch of high-speed railways (HSRs) overturned the “core–periphery” pattern formed during the era of conventional railways and shifted the core from the western region to the eastern one. Regional disparities in economic development in Fujian steadily declined over time. However, railway development was negatively associated with the convergence process, particularly in the developed east areas compared to the less developed west areas.</p>