首先从切应力和吸应力的角度，通过受力分析发现散体泥沙起动的主导因素是切应力；随后基于对黏性土起动现象的观察和对黏性土起动的试验研究，采用概化试验的方法试图诠释黏土与散体沙起动机理上的区别。试验证明了黏土起动中吸应力的存在，得到了垂线平均流速与吸应力的关系，并测得吸应力最大可达切应力的 941 倍。可认为吸应力是黏土起动的外在主导因素，黏土本身的抗拉强度是其抗起动破坏的内在因素。

Firstly, according to the force analysis of acting on a sand and the view-point of shear stress and suction stress, the author found out the dominant factor in the incipient motion of noncohesive sediment is shear stress. Secondly, the former researchers who followed the theories of noncohesive silt thought that the mechanism for erosion of clay is similar to noncohesive silt. They focused on the shear stress of clay and got many empirical formulas. The calculated results obtained by these formulas have greater differences. Finally, in accordance with the clay erosion process and its characteristics, the author designed an experiment in open-channel. The result of experimentation proved the existence of suction stress. Afterwards, the author got the relationship between suction stress and vertical mean velocity. The maximum suction stress is up to 941 times of shear stress. We draw a conclusion that the suction stress is the extrinsically dominant factor of clay erosion, the tensile strength of clay itself is the inherent factor that resists the destruction of flow.