Potential energy of water phase in unsaturated soils and corresponding change during the process of water be soaked into initially completely dry soils are discussed qualitatively. Then

based on water phase continuity requirement

generalized Darcy’s law and Gardner’s empirical equation on relationship between coefficient of hydraulic conductivity and matric suction

formulas are established and solved by finite difference method to calculate matric suction in unsaturated soils along depth in the condition of one-dimensional steady flow

respectively for permeation and for evaporation. Not only matric suction

but also head and coefficient of hydraulic conductivity can be attained easily by the proposed method.