论文从土壤水文学科视角来研究和分析黄土高原森林水文作用的两个重大问题，即对总径流量和对地下水转化的影响。联系黄土高原与水循环有关的生态属性，系统阐述了林地土壤下伏干层的发现、分布、水文性质及其生物学成因。重点分析了干层因其巨大水分亏缺量阻隔重力水下渗，阻止降水垂直入渗补给地下水的作用。指出森林因其显著拦蓄径流作用，蓄积水分又难以转化为地下水，因而具有减少林地出境总径流量的作用。

 From the research results on soil hydrology， the effects of forest hydrology on the total runoff and the surface water transferred into ground water were analyzed．It was found out that there exits an underlying drying layer of soil underneath forestland at a depth of more than 1 to 3 m from the soil surface．The distribution of the drying layer and causes why it exits are expounded， as related to ecological attributes of the Loess Plateau． It was believed that the drying layer is in great water deficit caused by evapotranspiration，which prevents gravitational infiltration of water and the replenishment of ground water．It is determined that a forestland on the Loess Plateau reduces the total runoff as the results of the increased retention of runoff and of the reduced recharged into ground water．