Abstract: The hydraulic conductivity function is the key parameter in the seepage analysis of unsaturated soil. Based on the foundational equation of fluid mechanics and the theory of probability and statistics,this paper proposes a theoretical model for saturated permeability function. This model can take the influence of soil structure into account. It is combined with the Mualeum(1976)relative permeability function model,together with the variation law of the structural parameters during deformation proposed by Assouline(2006). The influence of deformation on unsaturated permeability function is modeled. The paper compares the experimental results and some available models and the present model. The present model can improve the prediction precision without any increase of experimental workload. The necessities of applying statistic theory into soil mechanics is also discussed in the end of the paper.