As metropolitan areas expand spatially, they encounter constraints imposed by the fixed daily time budget. Rail transit enhances transport efficiency, reduces costs, and facilitates the formation of a “transit economic field” centered on rail networks, thereby alleviating such temporal-spatial pressures. This paper adopts an integrated temporal-spatial analytical framework. Following a conceptual clarification of the transit economic field, it dissects the mechanisms through which rail transit improves mobility and examines how this field influences urban spatial patterns, temporal dynamics, and their interrelationships. It constructs a theoretical framework to explain the co-development of transit economic fields and cities, supplemented by empirical case studies. The key findings are as follows: Firstly, the transit economic field represents a high-density development model that expands both horizontally and vertically around rail networks. It mitigates temporal-spatial conflicts. Secondly, with rail networks as the core, the field integrates diverse spatial functions, facilitating the establishment of economic connections and stabilizing temporal-spatial relationships. Thirdly, the transit economic field contributes to the preservation of urban natural ecosystems and enhances urban livability. Overall, this research can provide insights for promoting rail transit-oriented development transitions in large cities and urban agglomerations.