Abstract: In order to evaluate the stability of the mine slope of a certain open-pit copper mine under extreme conditions in Tibet，with the mining slope A-A profile as the typical research object，the rock mechanical parameters were gained through the rock and soil mechanics laboratory test and the experience analogy method，and the calculation model of slope A-A profile was established by ANSYS software.Then，loaded the heavy rains and seismic loading，the slope displacement，the shear strain increment and the plastic zone size were analyzed by FLAC3D software.The results showed that under the condition of excavation，the biggest cumulative displacement of gravel soil area is about 84.6 mm，and the facial shear strain increment is very small，which is under 0.001.The maximum shear strain increment of gravel soil slope steps rock is less than 0.009 36.There is no plastic zone on the rocky steps and in the gravel soil slope area，and slope step and local gravel soil slope area step are stable.Under the heavy rains and seismic condition，the maximum cumulative displacement is about 366.8 mm，and the maximum cumulative displacement of gravel soil area is about 84.6 mm，with very small facial shear strain increment of under 0.01.The maximum shear strain increment of local gravel soil slope steps rock is less than 0.082.Rock face has a small plastic zone，and the gravel soil slope steps of area has a larger plastic zone wit a lower stability.But the slope remains stable as a whole.

Key words: Open-cast mining, Slope stability, Heavy rain and earthquake load, ANSYS pretreatment, FLAC3D post-processing