Abstract: The mobility of redox sensitive nuclides is largely dependent on their valence state. The radionuclides that make the dominant contributions to final dose calculations are redox sensitive. Almost all the radionuclides (except ¹²⁹I) have higher mobility at high valence state, and correspond to immobilization at low valence state due to the much lower solubility. Pyrite is an ubiquitous and stable mineral in geological environment, and would be used as a low-cost long time reductant for the immobilization of radionuclides. However, pyrite oxidation is supposed to generate acid, which will enhance the mobility of nuclides. In this paper, the reaction path between U, Se, Tc and pyrite in the groundwater from Wuyi well in Beishan area of China has been simulated using geochemical modeling software. According to the results, pyrite can reduce high valent nuclides to a dinky-level effectively, with the pH slightly increasing under anaerobic condition that is common in deep nuclear waste repositories.