Abstract: A series of experiments on swelling pressure are carried out by using the conventional consolidation apparatus, and the effects of different concentrations of sodium chloride solution on the swelling pressure of samples with different initial dry densities are studied. The pore distribution of the samples after the expansive tests is investigated by NMR. The results show that the swelling pressure decreases with the increase of salt concentration under the constant dry density. The results of NMR show that the larger the salt concentration, the more the T₂ curve distribution moves to the right, which indicates that the larger pore volume increases and the smaller pore volume decreases. Under the same dry density, the Donnan osmotic pressure decreases gradually with the increase of salt concentration, which leads to the decrease of the swelling pressure. And with a constant volume, because the swelling pressure decreases, the internal swelling pressure decreases accordingly, so the volume of the pores being filled decreases, which leads to larger pores. So the T₂ curve of the samples with the same dry density moves to the right with the increasing concentration of salt solution.