Progressive toppling of rock slopes with fractured slab structures is quite common in the slopes of hydropower and highway engineering, posing a potential safety risk during both construction and operational phases. The field investigation found that progressive toppling mostly occurs on slopes with concentrated tectonic stress, intense river incision, and high steepness. Typically, these slopes are composed of hard, thinly-layered, and overthrusted rock mass with a fractured slab structure. From a macroscopic point of view, progressive toppling failure is neither a collapse nor a slide but a form of discontinuous deformation. The traditional limit equilibrium method for slope stability analysis is not suitable for evaluating such slopes. In this paper, by taking the progressive toppling of the slopes along the G108 Highway in the Qinling Mountains as an example and considering the uplift of the mountain and river downcutting, a discontinuous deformation analysis (DDA) method was employed to simulate the entire process of progressive toppling, and the mechanisms of its evolution were analyzed. The results show that as the river downcutting progresses, the rock mass experiences interlayer shearing along bedding planes under the influence of gravity, gradually tilting toward the river valley. Once a through-going rupture area develops, it transforms into a landslide failure. For the evaluation of such slopes, a numerical model should be used to simulate the entire deformation failure process. This allows for the estimation of the current state and development trends, providing a basis for reinforcement and management.