Since the experimental points of non-steady state method are often concentrated after oil and water both coming out, resulting in insufficient data of the oil-water front.The application of non-steady state method to medium-light oilfield may cause deviation, resulting in difficulties to accurately understand the law of water rising.In this paper, the traditional relative permeability model is improved,and the relative permeability calculation is carried out by using the oilfield production data to realize the encryption of therelative permeabilityin the low water cut period.The results show that the method is consistent with the experimentally measured data and can reflect the seepage law in low water cut period and is of strong guiding significance for obtaining relative permeability in medium-light oilfield.