【Objective】Soil shear strength is an apparent indicator of how easily shear deformation occurs under the action of external force, and a major index to characterize soil mechanical properties, as well as an important parameter of the process-based soil erosion model for prediction of hydraulic erosion, so it is very closely related to soil erosion. However, soil structure, water regime, biomass and particle size composition of a collapsing mound varies sharply with development of the collapse. So far, little has been reported on soil shear strength at each collapse developing stage. The purpose of this study is to (1) investigate variation of soil shear strength with the process of soil erosion on typical collapsing mounds; (2) determine influences of basic physical and chemical properties on soil shear strength; and (3) establish an equation for prediction of variation of soil shear strength with development of collapsing.【Method】The experiment lot was set up in the Jingouxing watershed in Tiancun Town of Gan County, where there are quite a number of collapsing mounds, diverse in erosion type. Three adjacent collapsing mounds of granite different in collapse developing stage (initial stage, active stage and stable stage) were selected for the experiment and a total of 15 sampling sites were set in the pattern of “Plum Blossom” or a pentagram for mixed sampling on each mound. Topsoil samples from the 0～20 cm soil layer of each mound and relevant environmental variables, were gathered, separately, for analysis of basic soil properties and soil shear strength. The data were processed with the classical statistic method for spatial variation of soil shear strength and variation of saturated shear strength with developing of collapse was predicted with the stepwise regression equation.【Result】(1) The physical properties of the soil in the collapse system are relatively poor with bulk density of the top soil layer varying in the range of 1.02～1.40 kg•m^-3 and declining with the position lowering along the slope, particle size composition coarsening, soil organic matter content lowering and root density ranging from 0.27 to 3.57 kg•m^-3, all of which demonstrate typical features of soil degradation with developing collapse; (2) Soil cohesion and internal friction angle, regardless of position along the slope, varies quite similarly, that is, both in a declining trend with development of the collapse, peaks at collecting areas, and bottoms in ditches. When collapse develops into a stable stage, restoration of vegetation promotes formation of root-soil complexes, which in turn increases soil cohesion and hence soil shear strength by a certain degree; (3) Statistical analysis shows that the contents of gravels, silt and clay are the optimal parameters to characterize soil internal friction angle of a collasping mound and their relationships can be well-described with a power function. Besides, a good linear correlation between root density and soil cohesive was observed; and (4) The experiment used root density and particle size composition to characterize shear strength of the soil under saturation, and established the equation (R²=0.891, P<0.01) for predicting soil shear strength of a developing mound.【Conclusion】All the findings listed above demonstrate that collapsed systems are generally poor in soil quality. With developing collapse, soil properties degrade obviously. Soil saturated shear strength varies significantly with soil particle-size distribution and root density across the collapsing erosion area, and is affected jointly by soil texture, topography, moisture and land use at the regional scale. It is recommended to use the functional equation based on parameters like particle-size and root density to predict soil shear strength, particularly for soil layers below 20 cm in the collapsed erosion areas in South Jiangxi. The study has discovered the main factors controlling soil shear strength in the South Jiangxi granite collapsing areas at different development stages, and provided certain theoretical foundations for further researches on mechanisms of soil shear strength responding to soil properties in expection of providing data of reference value and practical significance to future researches on control of soil erosion and rehabilitation of ecosystems in collapsing erosion areas.