In view of the current commercial numerical simulation software of chemical flooding is not suitable for low permeability reservoir，the mechanism of polymer flooding in the low permeability reservoir was studied by laboratory experiments. The key physical property parameters of polymer flooding in the low permeability reservoir in SINOPEC Jiangsu oilfield were characterized quantitatively，and the mathematical model of polymer flooding in the low permeability reservoir was established by using the pseudo-start-up pressure gradient and nonlinear model respectively，and the model was solved by numerical method. Research results show that the suitable relative molecular mass is 6 million to 9 million for the polymer flooding in the low permeability reservoir. The pseudo-start-up pressure gradient model ignores the bending section of the percolation curve and exaggerated the seepage resistance of the low permeability reservoirs，so the nonlinear model is more suitable for the simulation of polymer flooding process in the low permeability reservoir. The application in Sha7 block of Jiangsu oilfield shows that the numerical simulation method based on the nonlinear model can consider the influence of start-up pressure gradient for the polymer flooding in the low permeability reservoir，and the simulation results are consistent with the actual production data of the oilfield. It provides an effective technique and method for the optimization and dynamic prediction of chemical flooding in the low permeability reservoir.