Experiment of evaporation of soil water were carried out in the polymethylmetha-crylate cylinders with diameter of 5 cm and length of 200 cm.The water in soils on loessal plateau is mostly in the status of suspended water.Therefore,the upward movement of water by evagora}tian in souls on loessal plateau belongs to unsaturated flow.Under the unsaturated condition the evaporation process of soil water is considered the movement of one-dimensional vertical flow.