After prolonged development, most domestic and international oilfields have entered a late stage of high water cut and high recovery, with a comprehensive water cut reaching up to 90%. Carbon-oxygen ratio logging can directly distinguish oil layers from water layers with low salinity, unknown salinity, or significantly varying salinity in cased wells. This makes it highly valuable for detecting oil and gas layers and locating and monitoring oil-water interfaces. It is currently one of the most effective methods for determining residual oil saturation in cased wells. This paper is based on two carbon-oxygen ratio spectrum interpretation models (the fan and ratio chart methods). It compares and analyzes these two methods and optimizes the interpretation parameters in the ratio chart model using an improved genetic algorithm. The results are effectively integrated with reservoir and conventional logging interpretation results, reducing the impact of lithology and physical properties on measurement values. This provides a theoretical foundation for improving the interpretation capability and accuracy of carbon-oxygen ratio logging, allowing for quicker and more accurate identification of water-flooded layers. This technical support aids in monitoring oil-water dynamics, determining water-flooded layers, and enhancing production potential during oilfield development.