To study soil permeability of soil element within the high earth-rock dam under complex stress state, medium-sized triaxial tests are carried out on the medium-sized triaxial apparatus for three kinds of soils with different gradations from the same material site, which incorporates five levels of confining pressure(100 kPa、400 kPa、800 kPa、1 200 kPa and 2 000 kPa), with each being consisted of four stress levels(0、0. 2、0. 4 and 0. 8). The permeability coefficient of soil sample is determined by using constant-head test method when the sample deformation is basically stable in the initial stress state. The test results show that, the coefficient of permeability is largely influenced by soil grading. Under the same stress state condition, the coefficient of permeability appears to decrease with the increase of silt and clay contents. Moreover, this coefficient of permeability is gradually reduced by the increased confining pressure and stress level, the effects of confining pressures on the coefficient are remarkably intensified by a lower contents of silt and clay and higher content of soil with large particle. For soil samples with different gradations and the same compactness, the effects of stress levels on the coefficient of permeability are basically the same. Based on the analysis results of the coefficient of permeability varying with the confining pressures and the stress levels, an empirical formula is finally established to describe the the permeability coefficient of soil under complex stress state.