The dynamic behavior of a CECE column used for a demonstration reactor (DEMO) plant has been studied. In the case where the column was filled with natural water, the time required to achieve steady state was almost the same as that for the column operated under the total reflux mode. The manipulated variables were flow rate of the bottom stream for the control of the bottom tritium concentration, and flow rate of the hydrogen stream for the control of the top tritium concentration. For both the variables, the response curve was expressed by the first-order lag system, and a PID controller could be applied.