Abstract: Radioactive nuclide inventory calculation is the basis of radiation protection, shielding design and environmental impact assessment of the nuclear power plant. In order to improve the capability of HTGR radioactivity analysis, the NUIT nuclide inventory code was developed. Radioactivity calculation was conducted for fuel elements of HTR-10 and HTR-PM in specific burnup, and the results were compared with the reference results given by KORIGEN. The result demonstrates that the NUIT code can be utilized for HTGR’s nuclide inventory calculation with good precision and efficiency.