Abstract: The soft rock slope of open-pit coal mine in eastern Inner Mongolia has the situation of multi-side and multi-stage landslide. In order to solve the problem of systematic instability of soft rock slope, the slope stability control technology is proposed, and the typical open-pit coal mine in eastern Inner Mongolia is selected as the research object. By collecting the previous landslide cases of open-pit coal mine, the deformation characteristics of each side slope are analyzed. The failure modes of slope instability are summarized, and the concept of systematic instability of slope is proposed. Based on the physical and mechanical test results of mudstone in the study area, the mechanical characteristics of mudstone under different water content conditions were analyzed. The limit equilibrium method is used to analyze the slope stability under different water content conditions. The sensitivity of slope stability to mudstone water content in the south, west and north sides of open-pit coal mine in the study area is discussed, and the main influencing factors of systematic instability are discussed. In view of the systematic instability of open-pit coal mine in the study area, the fan-shaped steering mining method is designed to research on the optimization scheme of mining area turning. At the same time, the mining mode of “reverse mining-stage backfilling” is adopted to study the mining scheme of the first mining area. In the process of mining transition, the controlled mining method is adopted to study the controlled mining scheme of the second and third mining areas. The research shows that the systematic instability has the overall instability characteristics of single-sided multi-landslides or multi-sided multi-landslides. The typical landslide modes are “traction-sitting” and “sitting-traction-slipping”, and the scale of landslide has a trend of gradual expansion. In the normal mining process, groundwater is the key factor affecting the systematic slope instability, and the systematic slope instability will occur when the water content of mudstone is greater than 30%. Under coordinated mining and controlled mining, the mining efficiency can be improved and the risk of instability can be reduced, which is more advantageous than traditional reinforcement methods.