Grid upscaling is to keep the reservoir physical properties and seepage characteristics of the two models as same as possible before and after upscaling. Thus, the model after upscaling can achieve the same development effect as before upscaling. The permeability is upscaled by harmonic average and arithmetic average. It's found that the relationship curve between recovery degree and water cut after upscaling is different from that before upscaling. Based on reservoir engineering theory, a functional relationship between slope and intercept of Kro/Krw⁃Sw relationship curve and slope and intercept of water⁃oil ratio and recovery relationship curve is derived. Therefore, the phase permeability curve after upscaling can be deduced back. It's found that there is a linear relationship between the displacement distance of the phase permeability curve and the intercept of the fitting line of the water⁃oil ratio curve and the recovery degree curve. The displacement distance of the phase permeability curve can be calculated. The phase translation law is verified by using actual oilfield data. The error of water⁃oil ratio and recovery degree curve between after translation and before coarsening is 3.16%, and the precision is high.