Abstract: The special composition and structure of the soil in the collapsing gully create its special soil-water characteristics, which is the basic condition for the formation of the collapsing gully.In order to study the correlation between the formation of avalanche and soil-water characteristics and soil composition structure, the residual soil and completely weathered soil in thecollapsing gully and non-collapsing gully were selected, and the soil-water characteristic curves and k-ψ curves were compared to verify that the completely weathered soil in the avalanche area has such characteristics as large intake air value, poor water retention and large variation of permeability coefficient.Through the correlation and sensitivity analysis between the above properties and soil clay content, the controlling effect of mineral composition on soil-water characteristics is verified.On the other hand, according to the soil-water characteristics of soil, it is deduced that compared with the "network pore channel" of residual soil, the pore size of all weathered soil in the reverse collapsing gully presents two levels of differentiation, and has obvious "dominant channel", and the overall uniformity of pore channel size is higher.Furthermore, the accuracy of the derived inversion information is verified by SEM test, and it is also confirmed that the soil structure also has a controlling effect on soil-water characteristics.Finally, from the correlation of soil composition, structure and soil-water characteristics, it is concluded that the formation of collapsing gully is mainly subject to three points: (1) the matrix suction with the same water content is small;② Poor water retention leads to high strength erosion deterioration;③ Pore water pressure surge caused by high permeability.