Abstract: A method of analysing total reflux state is suggested to study the multicomponents ionic exchange equilibrium involved in the U (Ⅵ)-U(Ⅳ) redox cationic displacement chro-matography and a series of exchange equilibrium formulas for individual ions are derived. Based on these results, relation between ρand ρ which are determinate parameters for the single-stage separation coefficient is established as follows: Continued from p. 136)ρ=1-φ/1/ρ+φρ and ρ are the molar concentration ratio of U (Ⅵ) to U(Ⅳ) in resin and in liquid phase, respectively; φ is a function of the effective displacement percentageβ:It can be predicated from the above equation that ideal experimental conditions by which ρ→∞whileρ→0 can not be found.