Abstract: The permeability of soils is of importance in the engineering design and construction. For the clayey soils, the change law and mechanism of permeability in hydrochemical environment are not clear due to the complex physicochemical interactions between the clay minerals and pore water. To explore the effects of salt solution on the permeability, a series of variable head permeability tests are performed on the remolded clay samples. The results show that the variation of the permeability with the concentration depends upon the dry density. For the samples with the dry density of 1.4 g/cm³, the permeability increases firstly and then decreases as the concentration increases. However, the permeability of samples with the dry density of 1.5 g/cm³ decreases continuously. When the direction of seepage is reversed, the permeability of the samples changes drastically. The change of permeability is irreversible under the periodical variation of the pore water concentration. In addition, the measurement of the variation of pore structure in the soils with the salt solution concentration is conducted by the nuclear magnetic resonance (NMR) analysis. Based on the above experimental results, the effects of salt solution concentration on the clay permeability are explained from two aspects: pore plugging effects caused by fine particle migration and pore sealing effects caused by fabric change.