Ensuring financial sustainability through financial digital transformation constitutes an urgent requirement for urban rail transit enterprises, with business-finance integration serving as an effective enabler for such transformation. Addressing existing research gaps—where digital transformation studies in the rail transit industry predominantly focus on technological applications in specific operational scenarios but lack systematic financial digital transformation frameworks, while business-finance integration research lacks empirical validation in rail transit contexts and emphasizes unidirectional approaches—this study employs a case analysis methodology examining Guangzhou Metro's practical implementation to investigate pathways and outcomes of bidirectional business-finance integrated financial digital transformation. That findings demonstrate that synergistic advancement of conceptual/systemic reforms, methodological transformation, and ecological restructuring effectively promotes organizational integration, information integration, and value convergence between business and finance functions, yielding significant outcomes: enhanced accounting information quality, development of cross-functional finance talent, strengthened business support, and deepened strategic alignment; financial processing efficiency improvements are manifested in a 5-day reduction of month-end closing cycles, 44% increase in per capita transaction document processing volume, and 52% rise in per capita voucher creation volume; cost-effectiveness is demonstrated through an 8.6% labor productivity gain and 9.2% reduction in cost-to-revenue ratio; the pathway “top-down design leadership→bidirectional business-finance integration→ enhanced data governance→phased ecosystem synergy” proves effective in advancing financial digital transformation. This research establishes a theoretical framework and practical paradigm for urban rail transit enterprises to advance financial digital transformation.