During the drilling process of large displacement wells, due to the high horizontal-vertical ratio, the movement of the drill string underground is complex, resulting in severe wear on the casing wall and a reduction in casing strength, greatly affecting subsequent drilling and production operations. A casing wear efficiency model based on energy transfer was applied. The segmented method was used to determine the lateral force on the pipe string, and the crescent-shaped wear of the casing was analyzed. Based on the API (American Petroleum Institute) minimum wall thickness method, the crescent-shaped casing wear was simplified, and a method for predicting casing wear and calculating residual strength was established. Using this model, calculations were performed on a large displacement well in the South China Sea. The results show that lateral force is the main factor affecting casing wear, and reverse circulation drilling has a significantly greater effect on casing wear than normal drilling. The most severely worn section of the entire wellbore is the section with the greatest dogleg severity, where the risk of casing failure is highest, making it the critical section for implementing anti-wear measures. After the completion of the four-stage operation in this well, the depth of casing wear at the location of the maximum dogleg severity is 1.15 mm, and the casing strength has decreased to 58.24% of its original strength, but still meets strength requirements. The research outcome provides a basis and reference for the prevention and control of casing wear in high-displacement wells in the South China Sea.