Abstract: To meet the testing and calibration requirements of the flow-through tritium ionization chamber, radioactive reference gas DT with different activity concentrations should be prepared. With the aid of the tritium-containing heavy water moderator and resin purification system in the CANDU6 reactor of Third Qinshan Nuclear Power Co., Ltd., the moderator activity concentration was obtained by liquid scintillation counting measurement-electrolysis method, and the hydrogen isotope abundance of the electrolytic gas was analyzed by mass spectrometry, and with the implementation of the PVT exponential dilution method, a preparation device for ultra-wide concentration radioactive reference gas DT was developed. The device was designed with a catalytic-oxidation-liquid scintillation counting verification unit and an exhaust gas collection-reuse processing unit, while isotope infiltration and inner wall electroplating and other measures were adopted for sample preparation to reduce the adsorption-memory effect on the device wall. The device has the advantages of small size, wide activity concentration range, low adsorption effect of low concentration DT, low cross-contamination, and low uncertainty. The prepared radioactive reference gas DT has an activity concentration range from 4.0×10⁴~1.0×10¹⁴ Bq/m³ at the standard state, which can meet the needs of different types and applications of flow-through tritium ionization chamber testing and calibration in China.