The stability of the dam slope is one of the crucial indicators for maintaining the overall stability and reliability of the dam. The seismic stability response analysis of the dam slope involves a significant number of factors that introduce uncertainty, primarily including the stochastic ground motion and the uncertainty of the shear strength parameters of rockfill. Furthermore, the rockfill material is susceptible to strain-softening behavior at low confining pressures when subjected to ground motion, which exacerbates its progressive failure. Therefore, the assessment of seismic safety for dam slopes should give due consideration to this characteristic of rockfill material. This study extensively explores the influence of rockfill softening, stochastic ground motion, and the variability of rockfill shear strength parameters on the stability of the dam slope. Conducting probabilistic analysis in conjunction with the generalized probability density evolution method (GPDEM), the findings suggest that it is imperative to evaluate the safety characteristics of the dam slope by considering the coupled effects of stochastic ground motion, the variability of shear strength parameters, and the effect of rockfill material softening. Based on this, a preliminary dam slope failure classification was proposed, and a framework for dam slope seismic safety assessment was established.