Abstract: The deterioration and damage of red-bed soft rock under the coupling effect of water and rock is a complex and long-term process. To study the deformation evolution and dynamic mechanism at the micro-level of rock mass during the damage process, this paper takes the large-scale red-bed rockslide - Duanqu Rockslide in Nanjiang County, Bazhong City, Sichuan Province as an example, and selects the undisturbed samples of red-bed soft rock at the rear edge of the landslide as the research object. Through electron microscopy scanning and X-ray diffraction, the microstructure characteristics are clarified, and the dynamic model is inferred through mechanical calculation. This study systematically clarifies the inter-particle cement dissolution and softening process caused by the coupling effect of water and rock, confirms that the dissolution and shedding of the cement phase is the essential cause of the expansion of the internal pore network of red-bed soft rock, and reveals the damage paths of dynamic and static water pressure during the damage process, as well as the damage mechanism of their synergistic effect. Based on the above findings, the research results establish an interface damage analysis framework for red-bed soft rock under the action of water and rock, establish a micro-interface evolution model, and based on Fick's second law, derive its theoretical equation, providing a theoretical basis for the quantitative assessment and prevention and control of red-bed soft rock engineering disasters.