Abstract: The disintegration of red bed soft rocks induces significant rock fracture phenomenon, which often leads to slope instability, rock falls and other adverse geological phenomena. In order to understand the soil-water characteristic curve (SWCC) and the disintegration characteristics of mudstone of Leshan mudstone,three suction control or measurement methods are used: filter paper method, continuous immersion and drying-wetting cycle. The results show that (1) The SWCC curve of the mudstone is a unimodal curve, and the matrix suction increase with the decrease of water content. (2) By comparing with various calibration curves and fitting typical models of many scholars, the correlation between the sample matrix suction fitting results is good（R²=96%）, and the Fredlund & Xing model can better simulate the mudstone（R²=96%）. (3) The experiment of continuous immersion in water and alternating dry and wet water immersion shows that the rapid disintegration is 0-6 hours, the slow disintegration is 6-12 hours, and the long-term disintegration stage is after 12 hours. Alternate wet and dry immersion can accelerate the disintegration rate of mudstone in the initial hydrophilic stage, but it has little effect on the final disintegration amount. (4) The variation range of particle size after water immersion and disintegration is mainly concentrated in 2~20mm, and the gradation curve D₆₀, D_30, D₁₀, and C_u decrease with the increase of water immersion time, indicating that with the increase of water immersion time, there are particles in mudstone. diameter decreasing trend. (5) The fitting formula of the shale disintegration resistance index y=1.17e^–0.22x, and the fitting degree is good（R²=96%）. According to I_d2=0.76, it can be seen that the disintegration of mudstone in this area is weak to moderate disintegration. The results can provide certain quantitative data support for the water-soil characteristics and disintegration characteristics of mudstone in this area and theoretical support for engineering construction in this area.