Abstract: The strength attenuation characteristics of the weak interlayers are one of the key factors leading to instability of the bedding rock slopes. In this study, the Nanbang slope of Fushun west open-pit mine was selected as the research object. A two-dimensional discrete element model of the Nanbang bedding slope was established using the UDEC numerical simulation method in combination with the discrete element theory, and the strength attenuation characteristics and large deformation law of the weak layer were studied. The residual strength decay curve of the weak layer over time was obtained by fitting the results of triaxial tests conducted under different confining pressures, and the FISH language was used to implement the attenuation of weak layer strength during numerical calculations according to the fitting equation. The numerical simulation results showed that deformation first occurred at the toe of the slope. As excavation continued, the strength of the weak layer gradually decreased, resulting in the trailing edge of the slope top being pulled apart, and the original stress balance being destroyed. Eventually, the landslide body slides along the weak layer. By establishing a backfilling numerical model for slope stability, it was found that after backfilling with a presser foot for 100 m, the slope stability coefficient had significantly improved, and the slope was in a basically stable state.