There is no economical exploitation value when water cut of oil wells reaches 98% during the process of water flooding after polymer flooding. But the injection and production systems are still in good condition. Core data shows that there are about 21.2% remaining oil which mainly exists in low permeability zone. There are a great mount of residual polymer in place after polymer flooding. According to data analysis, there is 72.3% residual polymer left in the central well block in Bei-1-Duanxi. Water fingering that caused by mobility ratio differential and formation heterogeneity in subsequent water flooding reduces the sweep volume greatly. How to take charge of the residual polymer to conquer water breakthrough and enhance oil recovery after polymer flooding gives us a great challenge.