Abstract: In order to study behaviors of adsorption and desorption of tritium on HTGR’s nuclear graphite, density functional theory (DFT) was used in this work. With the demonstration of equivalent characteristics of hydrogen and tritium in the sense of electronic structure, through theoretical calculations, the binding energy of tritium on the nuclear graphite was obtained. By analyzing the model, the adsorption and desorption mechanism and fraction of tritium on the nuclear graphite were clarified, and the cumulative amount of tritium at the end of the HTR-10 two decades’ life and the value of released tritium on accident condition were given. The results in this paper are useful to raise a new thinking to understand release mechanism of tritium in HTGR.