From the dual perspective of supply and demand, this study takes the 11 prefecture-level cities of China’s Jiangxi Province as research subjects to measure and project the demand-side security level, supply-side security level, and their evolutionary trends for enterprise employee’ pension insurance from 2025 to 2045. It systematically analyzes the spatial pattern of pension security across the three major regions of Jiangxi: northern Jiangxi, central Jiangxi, and southern Jiangxi. The findings are as follows. First, the demand-side pension security level in all prefecture-level cities has been rising continuously, with a “catch-up effect” observed among late-developing cities. However, the absolute disparity in demand-side security levels among cities has continued to widen, while the relative disparity exhibits a U-shaped evolution, with pronounced hierarchical rigidity. Second, the provincial pension supply can fully cover the demand without systemic shortfall. Nevertheless, the surplus margin—defined as the supply-side security level minus the demand-side security level—shows significant spatial differentiation. Cities such as Yingtan and Ganzhou face medium- and long-term tight balance risks between pension supply and demand, representing weak links in the regional pension system. On this basis, this study proposes countermeasures including the establishment of a differentiated dynamic adjustment mechanism for pensions and the improvement of a provincial-level fund coordination and reallocation system.