To support Chinese Inertial Confined Fusion research, a thermal cycling absorption process (TCAP) system was previously developed for protium removal from D–T fuels. However, to monitor the product quality in each TCAP cycle (10 min), an on-line analysis method is required. At ITER, the Analytical System is an individual system used, which meets the static analysis requirement via interconnecting lines. In this study, to meet the dynamic analysis requirement, a new on-line micro gas chromatography system is installed in this system glovebox and is directly connected to the sampling point. For proximity to the sampling point, its sampling valve is connected with two 10-cm, 1/16-inch stainless steel tubings. Two six-port valves are combined to perform the sampling cycle of “vacuum-loading-injection.” A 30 m MnSO₄ deactivated alumina metallic PLOT column is prepared for sufficient resolution of hydrogen isotopes at 77 K. The results show that the D₂ retention time is 3.6 min, and that the resolutions between H₂ and HD and between HD and D₂ were 1.5 and 3.8, respectively. The estimated lower detection limit of HD was 20 ppm for a sampling volume of 1 cm³. The times of sample loading, sample injection, and vacuum were 1, 0.5, and 2.5 min, respectively. A D–T mixture testing is in progress.