Abstract: Through the test of the undisturbed soil samples from Zhongyun River,Changxing Island of Yangtze River,and the water channel of Huaihe River to sea,it is considered that the critical starting condition for soil in different channes are different because of the difference of the formation conditions,qualities and structures,though the physical and mechanical proper ties of soil is similar. However,for the same river,the obvious regularity exists in critical starting condition and the physical and mechanical indexes:the critical starting condition of the muddy cohesive soil increases with the decrease of the shear strength and decreases with the increase of the moisture content;the critical starting condition of silty clay is the minimum, and the relation of the clay,the shear strength and the moisture content is nonlinear;and the critical starting condition of the cohesive soil increases with the increase of the shear strength and the moisture content.