Abstract: The "erosion - bank collapse" of soil bank slopes is currently the most prevalent and increasingly severe disaster problem in mountainous reservoir areas. Establishing its geomechanical model will be the key to predicting and preventing such disaster problems. This research takes the soil bank slopes in the Wushan - Badong section of the Three Gorges Reservoir Area as the research object. Through field investigations, theoretical analyses, indoor geotechnical tests, and model tests, a geomechanical model of "erosion - bank collapse" for soil bank slopes is initially established. The results are as follows: The main bank collapse modes of the soil bank slopes in the Three Gorges Reservoir Area are clarified as collapse - sliding type and progressive erosion type. The characteristics of bank collapse and material composition of the two types of collapse modes are summarized and analyzed through typical cases. Considering the physical and mechanical properties of the soil on the bank slopes and hydrodynamic conditions, a "erosion - bank collapse" geomechanical model of the soil bank slopes in the Three Gorges Reservoir Area is initially established. "Erosion - bank collapse" model tests of the two types of geological models under the action of waves are carried out. The results show that the collapse modes of the two types of model tests are consistent with the field investigation results, verifying the reliability of the geomechanical model in this study. For the collapse - sliding type of bank collapse, wave erosion niches are locally generated first. With the connection of the wave erosion niches, the bank slope collapses or slides under the action of gravity. For the progressive erosion type of bank collapse, wave erosion niches are mainly formed due to wave scouring in the initial stage. As the erosion process accelerates, wave abrasion eventually dominates. This research can provide technical support for the prediction and prevention of geological disasters in the reservoir banks, and has certain theoretical value and important promotion value.