Gaomiaozi bentonite has been identified as the proper buffer/backfill materials of the high-level radioactive waste geological disposal in China. It’s significant to study its mechanical properties and applications to design the repository more reasonable. UH model for bentonite is proposed based on the UH model for unsaturated soils. By considering the expansion of the soil aggregate, the model is suitable for unsaturated bentonite. Based on the user subroutines, UH model considering the expansion of the bentonite has been developed in finite element software using the semi-implicit algorithm. 3D numerical simulations of the deep geological disposal are carried out with ABAQUS using the proposed model. The analysis of the seepage field and stress field are made preliminarily. The results show that the inner stress of the bentonite in the repository is increasing. Also, a good stability of the disposal repository can be noticed from the simulation results when using the Gaomiaozi bentonite as buffer/backfill material. Based on the above analysis. The Gaomiaozi bentonite is proved to be a reasonable buffer/backfill material; and the subroutine is proved to be valid by the numerical simulation.