Abstract: The slope stability during transition from opencast into underground mining is one of the key techniques and the core issues in safe mining production.Based on engineering project，the numerical simulation analysis of discrete element method is applied to select appropriate mechanical parameters.With the use of 3DEC，Matlab and other software systems，the slope stability，slip deformation characteristics and follow trends of high slopes at underground mining are analyzed.As the result，Due to the combined impact of both underground mining and open-pit mining，the surface subsidence curves show as multiple sink basins of different sizes under superposition，so the rock slope deformation extent at different regions are different.According to the results of numerical simulation，the mining-induced displacement angle at underground mining area are different at the different exploitation stage，indicating that with different mining thickness，the damage level of the overlying rock is different.So during the transition from opencast into underground mining，the slope stability is mainly impacted by multiple factors such as goaf treatment and different mining thickness.Furthermore，the slope stability evaluation requires a combination of the specific circumstances of the mining.

Key words: High and steep slope, Transition from open pit to underground mining, Discrete element method, 3DEC, Slope stability