Abstract: According to hydrogeologic investigation in the fields and a developed experimental setup, seawater and freshwater were made to flow through a plexiglass column filled with samples from the downstream of the Dagu River. Water sensitivity at saline water-freshwater interface was studied by changing salinity sharply and gradually. The results showed that the permeability of porous media decreased by 64% when seawater was flushed by freshwater. However, the decrease of permeability was comparatively slow and the permeability decreased by 50% in the case of gradual salinity decrease. The faster the rate of salinity decreased, the larger the reduction degree of the permeability was. A significant decrease of hydraulic conductivity was observed with time and the decrease was irreversible. Due to rapid salinity reduction of the influent, the migration and interception of the released clay particles such as illite, kaolinite and chlorite resulted in the permeability change.