Abstract: Permeability coefficient of soil is extremely important to dike and dam engineering. Scale-invariant space of seepage failure testing soils were statistically analyzed by multifractal dimensions, which shows that fine particle content is the major factor of mass fractal dimension. Based on a pipe bundle model of porous medium, the theoretical relationship between permeability coefficient and porosity was deduced, indicating that the influence factors of permeability coefficient include fractal coefficient, particle size, fractal dimension and fluid viscosity coefficient. The nonlinear relationship of permeability coefficient, porosity and fractal dimension was verified for further studies based on seepage failure experimental results. The results show that when the fractal dimension value is greater than 2.83, porosity decreases obviously with the increase of the fractal dimension, while permeability coefficient decreases insignificantly under the cohesive force of hydroscopic water and film water. The results provide a theoretical base for seepage formation mechanism and evolution process, which can decrease the seepage disaster risk of dams.