Abstract: Nierji Reservoir is located in the alluvium and diluvium of Q1 with varied thickness.Based on the investigation of downstream of auxiliary dam on the right bank,the laboratory test and field test,we conclude that the permeability law of clay band is different from Darcy Law because of the existence of bound water.The main influence indicators consist of mineral composition,chemical composition,microstructure,specific surface area,granule,etc.On the macro level it shows as clay permeability, I0 and height of capillary rise.