The environment of the high-level radioactive waste repository is relatively complex. When evaluating the safety of the repository (disposal container, buffer material and surrounding rock), numerical simulation must be conducted, in which unsaturated Thermo-Hydro-Mechanical (THM) fully coupled numerical model should be used. A saturated-unsaturated THM fully coupled numerical model of geotechnical materials is established. Based on the Comsol Multiphysics software platform, the high-level radioactive waste repository is simulated for 500 years, in which the experimental data from the candidate area of the Beishan high-level radioactive waste repository in China and the Gaomiaozi bentonite are used. The results show that temperature in coupling simulation is 13 degrees Celsius higher than that in uncoupling simulation. When the water table rose from 0 m to 1,000 m, the time it took to fully saturate the buffer material fell from 703 to 28 years. The saturation time of the buffer material increases from 28 years to 250 years when the permeability of the surrounding rock decreases by five orders of magnitude. Each physical field is coupled to each other, which affects the long-term stability of the repository.