Abstract: Using the chelating displacer NTA containing Various concentrations of ammonium ion, separation of rare earths Y; Sm and Nd on the hydrogen bed has been performed with high pressure ion-exchange displacement chromatography, and a study on the influence of ammonium ion on phase composition yielded an empirical formula for calculating the phase composition in NTA system. When using Cu2+-retaining bed instead of H+-retaining bed, the displacement ion passing through the Cu2+-retaining bed has been found to play a part neither in displacing the band of rare earth nor in taking part in ion exchange equilibrium, but the influence of the displacement ion residual concentration on the phase composition of the Cu2+-bed is the same as that on H+-bed.