Abstract: A large-scale tritium calorimeter with a specimen cell (195 mm×420 mm) was designed and made. The lower measuring limit of specimen thermal power is 6 mW by this calorimeter. The correlation coefficient between thermopile signal output and specimen thermal power is greater than 0.999 9 when specimen thermal power is in the range of 160～3 500 mW. The measuring accuracy of the calorimeter is better than 0.2% when specimen thermal power is not less than 160 mW. Tritium can be measured when specimen is set asymmetrically in specimen cell. Tritium in large capacity uranium chemical bed was measured using the calorimeter and the result shows that the good precision can be expected.