Abstract: For the absolute measurement requirement of trace tritium activity in ITER-TBS system, a micro-calorimeter was designed. The solid tritiated samples were used to demarcate the output thermal potential（E_out） and the input thermal power（P）. The results show a good linear relationship between E_out and P, and the sensitivity coefficient reaching 0.13 V/W. The minimum detection limit of micro thermal meter is below 0.2 μW, and the calorimetric cup volume is more than 500 mL. The performance is expected to have a good application prospect for quantitative measurement of the trace tritium activity under various complicated situation in ITER-TBS system.