Abstract: Dry Surface Layer (DSL), which affects water circulation of lands, is one important part of the land-atmosphere interface in arid and semiarid regions. Directed by basic theories of soil physics, dynamics of soil moisture, soil thermodynamics and hydrogeology, based on synthetic analysis of document data of forefathers, combining parts of observation data of a physical test indoors, the concept of DSL was firstly defined, then its connotation and extension were discussed. Secondly, the relationship between DSL and Soil Dry Layer Underlining (SDLU) was compared. Thirdly, the relationship between DSL and depth of water table, and influence of DSL on precipitation infiltration, evaporation and vegetation was clarified. All these can enrich theories of DSL formation and earth’s critical zone, and provide scientific evidence for sustainable utilization of water resources and eco-environment protection in arid and semiarid regions.