Roadbed along the river suffers from water erosion at the bottom and collapse at the top under flood scouring, which leads to the suspension of upper pavement slab. In order to ensure the safety of roadbed along the river, this study explored the development mechanism of roadbed damage by flood in actual cases, and proposed the evolution process of instability under roadbed scouring. The stability law of roadbed along the river under flood scouring was analyzed, and the stability safety factor was corrected to analyze the sensitivity of water depth, flow rate, river bending angle and stability safety factor K in working conditions. The sensitivity of width and height of roadbed after flood scouring to water depth, flow velocity, river bending angle was investigated. Moreover, numerical simulation was carried out to determine the displacement nephogram and maximum shear stress nephogram of roadbed along the river under the conditions of road surface and roadbed load, vehicle loading or constant change of water depth. By comparing the above theories and engineering cases, the water damage mechanism of roadbed along the river was further verified.