Chemical flooding is an important technical measure to improve ultimate recovery in water flooding oilfield, and the molecular weight and concentration of polymer are important contents in the design of chemical flooding formula.Aiming at how to determine molecular weight and concentration of polymer, theoretical calculation and injection evaluation experiments in natural cores are carried outand the results indicate that the technical limits of molecular weight of polymer and applicable concentration range corresponding to the permeability of rock can be calculated rapidly by theoretical method.The critical value of molecular weight and concentration matching reservoirs can be determined simultaneously in injection evaluation experiments.The critical value of molecular weight determined by injection method, which represents the reality in reservoir, is basically the same as that of theoretical calculation.The polymer molecular weight can be determined by theoretical calculation and injection method,and the polymer solution concentration can be determined by viscosity ratio and injection method.At the same time, the viscosity loss of polymer solution in the course of injection should be considered.The targeting injection experiment is needed in different reservoir with different physical properties to determine polymer parameters.So using injection experiment with theoretical calculation is an effective method to determine polymer parameter, and the result can provide reference for the design of chemical flooding schemes.