Polymer flooding is an important means of enhanced oil recovery. Currently, the widely used polymers are mainly partially hydrolyzed and hydrophobic associated polyacrylamide. However, their slow dissolution rate and high viscosity seriously affect the efficiency of mining injection and production. A novel polyhydroxy polymer P(AM-DPMOH2) and polyborate compound (BPEI-3) were used to construct a borate ester bond binary composite system, and the dynamic covalent bonds formed between the polymers can undergo reversible reactions of bonding and breaking under the influence of reaction thermodynamics. The effects of pH, temperature, salt concentration on the oil recovery performance of the system were evaluated. The results show that under neutral conditions, P(AM-DPMOH2) and BPEI-3 can dissolve quickly, and the viscosity of the solution is low, which makes the binary composite system easy to prepare and pump. Under alkaline conditions (pH ≥ 9), P(AM-DPMOH2) and BPEI-3 can form borate ester dynamic covalent bonds and increase viscosity, establishing effective flow resistance in the core. The resistance coefficient is close to that of partially hydrolyzed polyacrylamide (HPAM) solutions with similar viscosity, and the residual resistance coefficient is higher than that of HPAM. The oil recovery experiment results of heterogeneous core at 75 ℃ show that the composite system improves oil recovery by 7% more than HPAM. The injection process of pre-alkaline environment followed by composite system flooding using alkaline flooding was studied to achieve the application scenarios of low viscosity on the ground and high viscosity underground in the composite system, providing new ideas for improving the practical application efficiency of polymer flooding.