[Background] Collapsing gully, a serious soil erosion phenomenon in granite areas of South China, occurs mainly on mound or hill slopes under the interaction of water and gravity, causing severe destructions and threats in a wide range, including Hubei, Hunan, Jiangxi, Anhui, Fujian, Guangdong, and Guangxi, mainly south to the Yangtze River, and hence a grave impact on the economy in these hilly regions. [Methods] In order to explore the relationship between the soil moisture and the development of the collapsing gully, a field survey and indoor analysis were used to investigate the relationship between the soil moisture and the collapsing gully. The soil water characteristic curve of granite was simulated by fractal theory with Brooks and Corey model. The samples of profile ( surface soil, red soil, transition layer, sand layer, and debris layer ) in granite collapsing gully of Tongcheng County were collected, and the relationship between fractal dimension and soil particle size were analyzed by measuring the soil particle size distribution and soil moisture content. At the same time, the fractal theory of soil particle size was applied to simulate the soil water characteristic curve. Further, based on a comparison of estimated and measured results, the feasibility of estimating the soil water characteristic curve by fractal theory was explored. [Results] The higher the soil clay content in the profile of collapsing gully was, the larger the fractal dimension of soil particle size was; the larger the fractal dimension of soil particle size was, the larger the fractal dimension value of soil water characteristic curve was, indicating that there was a solid linear relationship between the two; the predicted values from the simulation of soil water characteristic curve by the fractal theory and measured values were in fine consistence, the accuracy of simulation results increased with the depth of soil increasing. The simulation effect was better for the soil containing less soil clay and silt content and more sand content. [Conclusions] The research results lay a foundation for the exploration of the mechanism of granite collapsing gully, which provides the guiding significance for the study of the water in collapse gully.