Abstract: Aiming at the problem of deformation and instability of dump slope with soft inclined composite basement in open-pit mine，taking Mengdong west No.2 open-pit coal mine as the engineering background，and based on the rigid body limit equilibrium method and three-dimensional numerical simulation method，the stability variation regularity of dump slope with different basement dip angles is studied，the instability mechanism of the stability of the soft inclined composite basement dump is analyzed，besides that，the corresponding control measures are given.The study results show that:①the slope stability is negatively correlated with the dip angle of the acclinal basement and positively correlated with the dip angle of the reversed dip angle of the basement；②the instability process of the slope basement can be divided into 5 stages，they are dump settlement，local shear dislocation，local shear failure， shear crack expansion and penetration；③the potential landslide mode can be described as intersection-bedding sliding，which taking the arc shape of the tensile crack of internal disposal material as side interface and the basement shear slipping as the bottom interface；④the stability of dump slope with reversed basdment is obviously better than that of the dump slope with conclinal basement，the analysis results of limit equilibrium method is well consistent with the numerical simulation results，which fully reflects the instability characteristics of the dump slope with soft inclined composite basement.On the basis of the above discussion，the stability control measures of the dump slope stability are further discussed.In order to improve the stability of dump slope under the condition of conclinal basement，the layout and development mode of local section dump lines and the order of stripped materials can be adjusted.

Key words: Open-pit mining, Dump slope, Inclined basement, Instability mechanism, Stability control, Limit equilibrium method