Desert can be divided into two types of sandy wilderness and sand land, according to different climate conditions.Sand land has relatively rich precipitation and integrated hydrological processes in cluding precipitation, evaporation, infiltration,runoff yield and flew concentration. However, there is only a little research on the hydrologic processes in sand land. Takingthe Tuwei River in the middle reaches of the Yellow River as a case, this paper analyzed water distribution and dynamicevolution in sand layer, and then developed an explicit and simple conceptual hydrologic model. The model is of convenientapplication and high precision. The results indicated that pore characteristics enable the storage of water without easy evapora -tion; the runoff distribution is well-proportioned annually and inter-annual variation is slight in this area, which results fromplenty of the ground water and strong ability of modulation. The fact that the basin is usually unclosed in sand land must beconsidered.