Abstract: Esheng open-pit mine of limestone in Sichuan province is taken as the study object, on the basis of the mine on engineering geological zoning, stereographic projection is used to analysis the failure modes of working bench slopes, ending stairs slopes, then numerical simulation method is used to analysis the failure modes of ending large slopes, finally the stability of the slopes of each area is evaluated based on the FLAC3D strength reduction method. The results show that: ① Under the control of discontinuities, there are 3 failure modes of working bench slopes and ending stairs slopes: wedge failure, collapse and bedding sliding.② Under the control of stratum, there are 4 failure modes of ending large slopes: bedding sliding, sliding-ripping, creeping-pressure induced ripping and flowing-ripping.③ in this study, for the dip slope, the stability coefficient of the two-dimensional model is larger than that of the three-dimensional model. As for the skew slopes, the result is just the opposite, and the average value of stability coefficient ratio of two dimensional and three dimensional model is 0.83.