Abstract: Infiltration and evaporation has great influence on matric suction distributions. Based on water phase continuity requirenent,generalized Darcy's law and Gardner's empirical equation on relationship between coefficient of hydraulic conductivity and matric suction, formulas are established and solved to calculate matric suction distribution in unsaturated soils in the condition of onedimensional steady-state infiltration and evaporation. In single unsaturated soil system, an analytical parametric study is carried out. Parameters,include α,infiltration rate q and q/k_s,are considered in the study.