It is required that the stakeholders work together to improve the balance between flow capacity and basin storage so that the flood control of the entire basin is increased. Therefore, it is necessary to analyze and visualize the relationship between water storage, infiltration, and runoff in a basin during heavy rainfall events. In this study, a coupling method of rainfall-runoff and flood flow analysis was developed to analyze flooding phenomena with rainfall as a given condition. Basin Water Balance Map showing the relationship between water storage, infiltration, and runoff in a basin is developed, and its application to flood control in a basin is examined. Specifically, we developed an analysis method that combines a tank model, which is a rainfall-runoff analysis method, and flood flow analysis, and applied it to the Toyohira River to demonstrate the usefulness of this analysis method and to show how the Basin Water Balance Map can be used.