<p>In order to assess the performance of bentonite-based buffer surrounding vitrified waste in a deep geological repository, it is essential to understand its thermal, hydraulic, mechanical, and chemical states, as well as their spatial and temporal evolution. From the perspective of hydraulic evolution, evaluating infiltration behavior in unsaturated buffer material is particularly important, as groundwater inflow significantly affects hydraulic conditions of buffer materials. In this study, sensitivity analysis was conducted to identify key parameters that strongly influence infiltration. The results indicate that the intrinsic permeability and the water retention function have a significant impact on the simulation of liquid saturation as key parameters to be focused on the hydraulic modeling. Furthermore, the results of hydraulic analysis for saltwater infiltration with various concentrations suggest that the hydraulic model is applicable for evaluating infiltration behavior within the fluctuation range, taking into account the uncertainties in the input values of the key parameters. This modeling approach, which focuses on the key parameters, has the potential to be a simple method to predict the hydraulic state transition of the buffer material during re-saturation period.</p>