Maintaining a reasonable liquid production scale is one of the main measures to delay the decline of production in waterflooding reservoirs during extra-high water cut period，during which the relative permeability curve of oil and water obtained from core testing is usually used to calculate the variation of dimensionless liquid production index with water cut，so as to predict the reasonable liquid production of reservoirs in extra-high water cut period. However，the theoretical dimensionless liquid production index curve based on core testing is not suitable for the actual situation in the field due to the great difference between the water flooding process in the core and heterogeneous reservoirs. Therefore，based on parallel core water flooding experiment，the dimensionless liquid production index curve equation with permeability and permeability ratio was obtained by regression，and the dimensionless liquid production index increment chart considering the influence of reservoir physical properties and physical heterogeneity degree was established. Then，the flow field of the water flooding reservoir was divided into water flooding swept area and non-swept area，and the experimental law of core water flooding was applied to the water flooding swept area only，and the dimensionless liquid production index chart of the reservoir with different sweep coefficients was plotted. Field example analysis shows that the method requires fewer parameters and is fast in calculation，can consider the influence of reservoir heterogeneity，and can calculate the current sweep efficiency of water flooding based on the measured fluid production index in the field.