Abstract: Based on the equation of percolation theory and introduction of Эфрос’s experimental results, and combined with oil-phase relative permeability formula proposed by Willhite and Chierici, hyperbolic, exponential and harmonic decline equations and the corresponding water-phase relative permeability formula are derived. The study results show that oil-water two-phase relative permeability relationships jointly determine the production decline equations in waterflooding oilfields; in the previous studies on the percolation theory of production decline equation, the oil-phase relative permeability formula was not the industrial standard relative permeability formula which should take the outlet water saturation as an independent variable, but a pseudo relative permeability formula taking the average water saturation as an independent variable. Finally, the actual applications of the new relative permeability formulas in Sanjianfang formation in Shanshan oilfield of Tuha basin, Sartu formation in Honggang oilfield of Jinlin oilfield and the lower section of E3s1 in Maxi oilfield of Dagang oilfield show that the actual production is basically the same as the results obtained from oil and gas relative permeability formulas, which could be a reference for the study on production declines in other oilfields.