Abstract: The theoretical simulation and experimental methods related to Long Lived Fission Product（LLFP） of ⁹⁹Tc and ¹²⁹I transmutation in nuclear spent fuel were studied in order to develop the feasibility research on ⁹⁹Tc and ¹²⁹I transmutation in XAPR reactor. ⁹⁹Tc and ¹²⁹I ACE format cross libraries in XAPR were generated by NJOY code based on ENDF/B VII.0 library, different parameters were analyzed. MCNP code was used to modify ⁹⁹Tc and ¹²⁹I capture cross sections by adopting new generating ACE format and CINDER’90 cross sections of 63 groups. Transmutation rates’ calculations of ⁹⁹Tc and ¹²⁹I in XAPR were done by ORIGEN2 code, as well as comparison with experimental data, the difference between theoretical and experimental data mainly comes from the deviation of neutron flux used and the actual one. Conclusions were made that XAPR is effective in transmutation of ⁹⁹Tc and ¹²⁹I.