近年来 ,以林草地地力衰退为特征的人工林草地土壤退化日趋严重 ,其中以土壤水分严重亏缺为特征的土壤干化现象愈益引起了人们的重视。土壤干化的直接后果是形成土壤干层 ,导致土壤退化 ,植物生长速率减缓 ,群落衰败以至大片死亡 ,严重地威胁到中国中北方地区特别是黄土高原地区生态环境的建设。因此 ,研究和解决土壤干层问题已成为黄土高原植被建设的迫切任务。根据现有土壤水分资料 ,初步分析了延安试区植被下的土壤干层现状 ,对不同林草植被下的干层状况做了比较 ,并提出了解决土壤干层问题的意义 In recent years, the soil degradation of plantation grassland, characterized by the decline of soil fertility of grassland, has become more and more serious. Soil drying, characterized by serious soil water deficit, has drawn more and more attention. As a direct result of soil drying is the formation of dry layer of soil, leading to soil degradation, plant growth slowed down, community decline and even death, seriously threatening the ecological environment in central and northern China especially the Loess Plateau. Therefore, researching and solving the problem of soil dry layer has become an urgent task of vegetation construction in the Loess Plateau. According to the available soil moisture data, the status of soil dry layer under vegetation in Yan’an was preliminary analyzed, the dry layer conditions under different vegetation were compared, and the significance of solving the problem of soil dry layer was put forward