Abstract: The disintegration damage of granite weathered soil is the most dramatic in the red soil,which is related with its own mechanical properties.The paper researches the mechanism of water-soil action in the disintegration from softening and slaking.The intense softening and slaking of granite weathered soil is supposed to be relative to its structural and unsaturated characteristics,the softening of granite weathered soil is deemed to decompression softening and damage softening,the no uniformity of grains and void characteristics of granite red soil,which cause suction imbalance in the process of soil wetting,that is the crucial reason to the red soil disintegrates.The softening and slaking of the soil is the internal cause of disintegration damage,and the long-term erosion of water and gravity is the external factor,which provides the sustained development power.Under the above internal cause and the external factor combined action,the collapsed the collapsing topography formed finally.