Oil-water relative permeability curves play a crucial role in water flooding evaluation and remaining oil potential assessment during the middle and late stages of waterflooding development in oil fields. Currently, relative permeability curves are primarily determined through laboratory experiments. However, due to reservoir heterogeneity and experimental limitations, core-measured oil-water relative permeability cannot accurately reflect actual reservoir production characteristics. To obtain oil-water relative permeability curves that accurately reflect the flow characteristics of medium-light oil fields, this study developed an inversion method by coupling the fractional flow equation with a novel characterization formula for oil-water relative permeability curves, based on the ratio relationship of oil-water relative permeability. The method enables re-evaluation of water flooding in actual reservoirs based on the relationship between water cut and oil displacement efficiency. Results show that, compared with relative permeability curves obtained from core displacement experiments, the inverted curves yield higher oil displacement efficiency at the same water cut, with a significantly slower rate of water cut increase. The inverted relative permeability curves based on dynamic production data can more accurately reflect actual reservoir characteristics and oil-water flow behavior. The inverted oil-water relative permeability curves were applied to classify water flooding severity and identify remaining oil potential in the oilfield. This effectively guided the formulation of perforation schemes and the deployment of infill wells. This study provides theoretical support for adjustment and potential exploitation during the late stage of waterflooding development in medium-light oil reservoirs.