Abstract: A model for the unsaturated soil hydraulic conductivity is established based on an assumption that the soil can be represented as a continuum fractal porous medium.The model contains three physical parameters : a coefficient λ, the fractal dimension D and the critical volume fraction α_c.The saturated and unsaturated hydraulic conductivities are connected by the parameter λ.The fractal dimension (D) represents the soil porous structure and the critical volume fraction (α_c) which accounts for the differential porosity from the smallest pore size for continuous flow to the largest pore size in the soil.The unsaturated soil hydraulic conductivity estimated by the model is compared with the experimental data of various soils.