Abstract: Water drive curves are the inherent characteristic curves of waterflooding. Based on the non-piston linear theory model of two-phase flow, a new water drive curve is derived, i.e. Np=A-B/(Lp+C) 0.5 . Theoretical study show that the coefficient (A) in the new water drive curve equation is closely correlated with reserves that can be put into production (Nom), i.e. Nom = A, while the coefficient B is in close relation with reserves in place (N), i.e. N=a B 2/3 . Examples are given to verify theoretical study results. The new water drive curve equation has higher accuracy than that of the current commonly used equations.