Soil aridization has turned into an important restricted factor on ecological construction in Loess Plateau.It is believed that loess in China is an indicator of the arid and semiarid climate.The development of loess deposition is a symbol existing the general tendency of climate aridization in North China from the Early to the Late Pleistocene.Loess as the parent material of modern loess soil has a significant influence on soil development and its properties can be reflected in modern loess soils. Taking environment aridization with loess deposition and three weathering type of loess formation as a start ing point,loess geologic origin of soil aridization in Loess Plateau was explored through comparative analysis between the old and present time.Soil physical cause of soil aridization is discussed in the paper.Soil aridization in Loess Plateau is the result of common influence of transient and immanent condition.Soil water physical properties,including water retention property and evaporation property, show an obvious regional directional change dealing with loess grain size composition,It means that soil water retention property gradually increases and soil evaporation property gradually drops from northwest to southeast.If the field capacity is taken as an index,and then soil water deficiency is discovered frequently in Loess Plateau.Arid soil-layer is the ecological aftermath of strengthened soil aridization resulted from the disturbing and breaking alignment of plant succession and ecological foundation of soil water.Based on analysis of climate change,prediction of soil aridization tendency in Loess Plateau is presented in the paper.