Beishan in Gansu province has been selected as the most potential area for the deep geological disposal of the high level radioactive waste. Considering the groundwater in the region containing the total dissolved solid (TDS)

NaCl – Na2SO4 was chosen as a dissolved solid. In this paper

one-dimensional swelling deformation tests and swelling pressure tests were carried out on Gaomiaozi sodium bentonite saturated by the salt solution with different TDS concentrations and distilled water. Based on the concept of the montmorillonite void ratio

the deformation characteristics of Gaomiaozi Na-bentonite at saturation were consistently identified in the salt solution and distilled water circumstances

respectively. The results show that both the relationships of the montmorillonite void ratio versus the swelling pressure and the dry density versus the swelling pressure are the straight lines and parallel to the condition of distilled water circumstance in the double logarithmic coordinates when the concentration of TDS is 12.3 g/l

and the swelling pressure in the logarithm changes linearly with the concentration of TDS. As a result

a method to predict the swelling pressure and deformation is given from the dry density of the buffer materials and the ion concentration of salt solution.