A specific example of the open-pit slope engineering was taken as the study object, on the basis of field investigation in open-pit slope and the understanding of the engineering geology, the engineering-geological zoning of open-pit slope and preferred joint plane of determining were carried out,meanwhile stereo graphic projection and limit equilibrium analysis method combining qualitative&quantitative, individuals and whole were used to analysis and estimate the safety&stability of excavation mine slope. The results show that:The sliding failure of bench slope in open-pit mine is less likely under the control of structural plane,the part of bench may collapse only under the influence of excavation disturbance, that is, the bench slope shows weak synergism.But mine slope system is in the range of synergistic stability,which is conforming the open-pit mine’s idea of moderate deformation and damage allowed of slope. It has important significance in arranging of construction and production management in mine site in the next stage.