Abstract: Thermal cycling absorption process (TCAP), a semi-continuous hydrogen isotope separation process, is of many unique advantages. TCAP system designed in this work mainly consists of a separation column, feeding and withdrawing subsystem, column cooling and heating subsystem, data collection and autocontrol subsystem. About 901 g Pd/K was packed in the column. The palladium mass content of the Pd/K whose particle sizes were 250-400 μm was about 40.8%. The hydrogen absorption capacity of the column was 27. 016 L（STP）. The system was tested in total reflux mode at different operation parameters including initial feeding ratio, cooling or heating temperatures, feeding place of raw gases in order to confirm the best operation conditions of hydrogen isotope separation. The results show that the higher initial feeding ratio and temperature difference of the column are, the better the separation effects will be when feeding at the midpoint of the column. If the gases are fed from the plug-flow reverser (PFR), the separation results will be better. The best one among the experiments is the one that fed 90% into the column from the PFR with cooling at 56 ℃ and heating at 290 ℃. The deuterium content in the product reaches 99.2% after 30 cycles. The protium contents in the raffinate and separation factor are 96.1% and 3 055.49 respectively after 60 cycles. Separation of protiumdeuterium was also done in online mode with the parameters of initial feeding of 90%, feeding and withdrawing of 3% during separation, cooling the column at 21 ℃ and heating at 290 ℃ in order to validate the separation capacity of TCAP. The results are not good because of the large gas resistance in the column, which may be induced from two aspects as Pd/K pulverization and jam of the column joint. So there are still some problems need to be solved in the construction of a TCAP facility and the hydrogen isotope separation in online mode.