Abstract: Polymer flooding is the most important method used to improve the oil recovery in the oilfield, it plays an important role in the 60 years Daqing Oilfield development, the oil recovery was enhanced to 13% more than that of water flooding. The main mechanism of polymer flooding is improving the flow mobility between water and oil, and increase the sweep volume, thus the oil recovery can be enhanced. In recent years, the mechanism that the viscoelasticity of polymer solutions can increase the micro sweep area in porous media and thus enhance the micro oil displacement efficiency has also been gradually investigated. Therefore, in this study, the characteristics, micro flooding experiments, core flooding experiments and the theoretical study of viscoelastic polymer are reviewed, and the current research status, experimental methods and approaches on the flow mechanism of viscoelastic polymer solutions are discussed. Then, it is shown that the normal stress generated by the viscoelasticity of the polymer solution can further pull and tug on the residual oil after water flooding, and promote deformation of residual oil, which can further improve the micro sweep efficiency and oil displacement efficiency in porous media than that of pure viscous fluids. The essence of elastic turbulence to cause apparent thickening is clarified, which has a certain positive impact on the improvement of oil displacement efficiency. Finally, the problems and development directions of the mechanism of viscoelastic polymer flooding are summarized, and the conditions of elastic turbulence, the contribution of viscoelasticity to the recovery of different types of crude oils in different sizes of pores, and the synergistic effect of elasticity and wettability have become the challenges and directions for future research. The paper can provide an important reference for the mechanism study of viscoelastic polymer solution and the selection of optimal polymer solution in the oilfield.