Abstract: Soil and water loss is serious in the Loess Plateau,and shallow surface landslides mostly occur in areas with well-developed vegetation after rainfall according to the field investigation. It is speculated that it is related to the disintegration which is the water sensitivity of the loess. In order to explore the mechanism of the disintegration of slope soil and the role of grass roots in disintegration,disintegration tests of root Malan loess and rootless Malan loess under different hydrodynamic conditions are designed. As a result,water enters the Malan loess and expands in the pores,cracks are generated and expanded and extended,and the soil body disintegrates and eventually breaks down. The effect of moving water on soil includes disintegration and transportation. The effect of still water on soil is mainly disintegration. The following conclusions are drawn:（1）The disintegration of moving water on the soil is more intense.（2） The disintegration of rootless Malan loess is determined by the pore structure. The roots grow along the pores and fissures,which improve permeability,form dominant flow in the soil,and weaken the disintegration of the soil.（3） Under the dynamic and static water environment,the root-bearing soil reduces the disintegration of the soil. Besides,the higher the rooting rate is,the more the disintegration is weakened.