Abstract: In order to investigate the behavior of permeability of rocks along complete stress-strain path, a series of laboratory tests for both hard and soft rocks under different confining pressure,pore pressure and seepage pressure have been performed. The test results show that the permeability of hard rocks is obviously different from that of soft rocks not only in permeability-strain behavior but also in value of coefficient of permeability.Comparing the stress-strain behavior with the permeability-strain behavior during the complete deformation process of the rock obtained from tests, this paper analyses the basic mechanism causing difference in permeability behavior between hard rock and soft rock, and reveals that permeability behavior depends mainly on the fracture form and character of rock.