To investigate the trends of change of viscosity and viscoelasticity during long distance migration in polymer flooding and to research the effect of the loss of viscosity and viscoelasticity on displacement efficiency, a series of laboratory physical experiments were conducted to simulate polymer flooding. A 30 m long sand packed model was built for the physical simulation. Following the injection, samples were obtained from sampling points along the model, and the properties of the samples such as polymer concentration, molecular weight and viscosity were analyzed. Based on the results, polymer solutions which have similar properties to the samples were prepared for the core displacement experiments. For comparison, glycerol solutions similar in viscosity were used as displacement agents in the same conditions. The results indicated that polymer concentration and molecular weight decreased with increase in the migration distance, and followed an approximately linear trend. The viscosity declined rapidly first, and then stabilized with the distance increase. The storage modulus decreased sharply in the near inlet area. Furthermore, the increment of displacement efficiency decreased with increasing distance, which was closely related to the loss of viscosity and viscoelasticity. This suggested that elasticity loss had a deeper impact than viscosity on displacement efficiency.  This research can provide a basis for the optimization of polymer flooding design.