Abstract: By changing the kind and content of clay mineral in the sand,associating with the simplex and replacing experiments for saline and fresh water,the water sensitivity characters of different clay minerals are studied in this paper.For the simplex fluid(saline or fresh water),the hydraulic conductivities of sand columns don’t decrease when the content of any clay mineral is under 1.5%(weight ratio),and only decrease by one digital grade even the content increases to 10% (weight ratio).The hydraulic conductivities of the sand columns containing smectite decrease more obviously than others containing kaoline and illite, whose decreasing extent is about 50% of the former’s.The result of the replacing experiment indicates that the hydraulic conductivities of the sand columns containing smectite decrease sharply,and the hydraulic conductivity is so low that the sand columns can be regarded as an impenetrable layer,but the other columns’ hydraulic conductivity don’t decrease greatly.The reason for this phenomenon is that the different clay minerals adsorb different quantity of water molecules and form to different quantity and size colloid agglomerates which bring on different varieties of the hydraulic conductivity.