Abstract: A thorough study on stability of an open-pit mining slope in Tibet is made.Based on the comprehensive analysis on the engineering geological conditions，and with the use of FLAC^3D numerical simulation software，the variation of displacement field and stress field in the rock slope under the excavation disturbance was studied.Research results show that the stepped excavation can truly simulate the impact of excavation disturbance on the slope stability; Under the effect of excavation disturbance，the rock mass unloading quantity and rebound deformation increases with the excavation depth added; The maximum displacement is situated in the middle-lower part of slope rock mass; The tension stress zone was formed in the vicinity of slope surface and the slope shoulder，and the slope toe shear stress increased significantly; The displacement field and stress field also exhibit “displacement steep rise” and “stress drop” phenomenon with the excavation proceeding.

Key words: Slope stability, Numerical simulation, Excavation disturbance, FLAC^3D