A major engineering challenge in construction projects lies in the stability assessment of rocky slopes with faults. The left bank slope of the Jinchuan Hydropower Station in the outlet field is notably influenced by the steeply inclined faults and rock joints, resulting in highly complex geological conditions and raising critical concerns regarding slope stability throughout construction and operation. The evolution mechanism of rock mass from fracture to deformation during slope excavation and unloading is determined using microseismic (MS) monitoring and numerical simulation. Results show that the MS activity can effectively reveal the influence of slope construction disturbance on geological structure damage and structural plane activation. Specifically, the g7 fault is a crucial factor influencing the failure mode of the left bank slope of the Jinchuan Hydropower Station in the outlet field. The comparison of monitoring data, numerical simulation, and in-situ failure demonstrates consistency between the deformation area of rock mass and the damage area defined by MS monitoring, confirming the accuracy of MS monitoring and numerical simulation results. Overall, the results can serve as a basis for the later-stage construction of the dam foundation slope at the Jinchuan Hydropower Station and provide guidance for the stability assessment of similar slope engineering projects.