The invention discloses a method of determining the polymer application concentration of polymer flooding, and belongs to the technical field of tertiary oil recovery in oilfield development. The method comprises the following steps: (1) according to the underground crude oil viscosity of a specific oil deposit and the temperature of the oil deposit, determining a mobility ratio required by polymer flooding under the oil deposit condition by using a system for doing a core oil-displacement experiment on the mobility ratio and enhanced oil recovery; and determining the viscosity retention rate of a polymer solution in the whole process of production from preparation of the polymer solution on the ground to the injection of the polymer solution into a polymer oil well; and (2) working out the viscosity value of the polymer flooding application under the oil deposit condition according to the mobility ratio determined by the core oil-displacement experiment and the viscosity retention rate of the polymer solution in the injection and production process, and then determining the polymer application concentration of the polymer flooding according to the relation between the viscosity and concentration of the polymer solution. The method is suitable for oil deposits with the temperature of 40-80 DEG C, wherein the viscosity of the underground crude oil of the oil deposits is in the range of 2-1000mPa .S, and the concentration of polymer is in the range of 600-2500mg/L.