This thesis deals with the development of a simplified ion-exchange dynamic model which can be easily applied to multicomponet ion exchange system. Numerous papers published before have shown that it is very difficult to apply the existign ion exchange models to the multicomponent ion exchange system such as demineralizers in nuclear power plants. Therefore the main objective of this thesis is to develop a theoretical model applicable to such systems and to predict the effluent concentration histories by utilizing it. In the model, the ionic fractions of the individual ionic species involved in solution or ion exchanger are expressed as the average values in each phase, and the ion exchange process is described in terms of a first-order kinetic reaction between the ionic species. This approach results in a first-order rate expression which represents the exchange rate as a function of contact time between two phases. The differences in the exchange rates among the ionic species can be explained in terms of ``equilibrium rate coefficient.`` In a given binary ion-exchange system, one binary equilibrium rate coefficient determines the exchange rates of two counterion species, and the equilibrium rate coefficients in multicomponent system are expressed by the linear combinations of the corresponding binary coefficients. A numerical method, based on the theoretical model, is developedi n order to predict the effluent concentration histories. The numerical method is validated by performing the relevant column experiments and comparing with an existing local equilibrium method. The results show that the developed model predicts the effluent concentration histories and the validity of the model quite accurately.