Abstract: After the implementation of Pingtan and Minjiang Estuary Water Resources Allocation (abbreviated as the One Gate and Three Lines Project) in Fujian Province, complex competitive and coordinated relationships exist among the multiple demands for water resources in the water-receiving area. To reveal the competitive and coordinated mechanisms and establish quantitative conversion relationships among power generation, water supply and ecology, an optimization model based on multi-objective non-dominated solution set was constructed for the cascaded reservoir system consisting of Longxiang Reservoir and Jukou Reservoir in the Dazhangxi River Basin, with the objective functions solved using the NSGA-Ⅲ algorithm. Based on long-term series and typical-year calculation results from the multi-objective model, a qualitative analysis was conducted on the competitive and coordinated relationships among power generation, water supply and ecological water demand in the cascaded reservoir system. Furthermore, the conversion patterns and quantitative relationships among water supply deficit, ecological water deficit, and the system′s multi-year average power generation were analyzed. The results indicated a significant asymmetric competition among the three objectives, with the most pronounced contradiction observed between power generation and water supply. Quantitative conversion formulas among the objectives under different inflow frequencies were established through multiple regression analysis, demonstrating good goodness-of-fit. This method can provide a reference for optimizing water resource allocation in water-receiving area and alleviating supply-demand contradictions.