The socioeconomic effects of the railway network on the Qinghai-Tibet Plateau (QTP) received wide attention, but most studies are qualitative studies with a short period and small spatial scope. We explored the impact of the plateau railway network on the internal and external accessibility and economic linkage of the QTP during 1984–2030. The average shortest travel time (ASTT) and the weighted average travel time (WATT) were used to measure the spatial railway accessibility. Then the gravity model was used to calculate the economic linkage between cities, and the contribution rate of the railway network to the growth of economic linkage was quantitatively identified. The ASTT within plateau cities decreased dramatically during 1984–2030. The WATT between the plateau cities and the 28 capital cities outside the plateau also decreased by 42.4–88.5%. The imbalanced economic development in different regions and their linkage to the QTP railway network increased the spatial inequity of accessibility in China's central and eastern regions from 1984 to 2030. The economic linkage between six plateau cities and 28 capital cities increased obviously. The contribution rate of railway construction to the growth of the total economic linkage increased substantially with the evolution of the railway network. For railway planning of remote areas, policymakers should consider railway accessibility and its socioeconomic effects and spatial inequity in the long term.