A novel water treatment process, combining cationic ion exchange and bicarbonate removal in a countercurrent three-phase fluidized bed, was explored. The study was based around a laboratory scale bed. The different operating conditions and effluent quality were investigated. The results showed that concentrations of sodium and carbon dioxide in effluent decreased with increasing height of resin static layer and greater airflow velocity. The concentration of sodium and carbon dioxide in the effluent was lower than 0.1 mg/l and 5 mg/l respectively. Instantaneous conductivity that illustrated effluent quality was measured in different sections of the bed. A mathematical modeling which can simulate the changing of conductivity was built, the validity and applicability of the model for future prediction of effluent properties have been verified by the good agreement between the experimental and predicted values.