Abstract: The soil structures, including soil particle mass(size) distribution, pore volume distribution and solid-ore interface roughness, are fractals in lin ited length-scales and m ay be represented by mass fractal dimension, pore volume fractal dimension and surface fractaldimension.The functional equations consistentwith the CampbellLaw have been established between fractal dimensions and the hydraulic properties of soils in literatures reviewed.The equations disclose thephysicalmechanign of theCampbellLaw andmay be used to predict soil water retention and hydraulic conductivity of unsaturated soil.