After a primary seismic event, subsequent aftershocks frequently induce progressive damage to slopes. Evaluating the response of slopes to mainshock-aftershock sequence (MAS) from a probabilistic perspective is crucial for disaster prevention and mitigation. Current research primarily focuses on single mainshock events, with limited consideration of the aftershock effects. Our study addresses the MAS events. Firstly, the random input field of the MAS is constructed through the collaboration of theoretical models and real data. Then, considering the peak characteristics, cumulative characteristics and spectral characteristics of the MAS, the numerical simulation method is used to explore the control parameters for the soil slope response. Ultimately, leveraging the probability density evolution method (PDEM), we introduce a reliability assessment framework for soil slope behavior under MAS loading. Compared with the existing approaches, the new method fully accounts for aftershock characteristics and assesses the degree of slope permanent displacement response with greater precision. These results offer substantial practical utility for engineering applications and serve as guidance for slope stability assessment and disaster mitigation strategies.