Abstract: To study the influence of the horizontal distance between underlying mined-out area and slope toe on the stability of open-pit mine slopes, the northern end slope of the first mining area in the East Open-pit Mine of China Coal Pingshuo Group Co., Ltd. was used as the engineering background. A combination of physical similarity simulation and numerical simulation was adopted, considering the distribution of the collapse zone and the fracture zone ("two zones") in the overlying rock of the mined-out area. The study analyzed the displacement variation of the overlying rock and slope stability coefficient under different horizontal distances between the mined-out area and the slope toe. The results indicated that: ① As the horizontal distance between the mined-out area and the slope toe decreased, the height of the collapse zone gradually increased, the fracture zone became more evident, and fractures in the overlying rock gradually extended to the slope surface. When small-scale cracks appeared on the slope surface, the slope reached an unstable state. ② With the reduction of the horizontal distance, a concentrated vertical displacement zone appeared in the overlying rock and gradually extended upward until it connected with the slope surface. The concentrated horizontal displacement zone tended to expand upward, and when it connected with the horizontal displacement zone of the slope, the slope became unstable. ③ Both the horizontal and vertical displacements of the slope surface increased as the horizontal distance between the mined-out area and the slope toe decreased. ④ The farther the horizontal distance between the mined-out area and the slope toe, the greater the slope stability coefficient, making the slope less prone to instability and failure.