Abstract: By using FeCl3-HCl as displacer (also as oxidizing agent), Ti(Ⅲ) as retaining ion (also as reducing agent), the cationic redox chromatography for uranium isotope separation is studied. An equation of steady migration rate is derived and confirmed, and a formula for the calculation of "effective" displacement ion concentration is suggested. It is shown by experiment and theoretical treatment that under the conditions of the present research, the "effective" displacement ion concentration is directly proportional to the concentration of displacing ion.The relations between the displacing ion concentration and the composition in liquid and resin phases of uranium band as well as the role of HC1 are studied in detail.