Abstract: In the phase of open-underground combined mining， the unreasonable selection of underground mining methods may disturb the stability of open-pit slopes and even lead to such disasters occurrence as slope instability， surface collapse and dumping landslide. These increases the maintenance cost of open-pit slopes and dumps. In order to reduce the disturbance of underground excavation on slope， and combined with the engineering background of a certain open pit phosphate mine， the finite element method of ANSYS is used to carry out the numerical simulation analysis. Through the analysis of the influences on the slope and isolation zone under the three conditions of non-excavation， upward horizontal slicing filling method and open-pit method， it is concluded that the change of the isolation layer is small when using the filling method for underground excavation. Local slopes are affected and may be damaged, it is necessary to strengthen the protection measures for the slope. When the empty field method is used, the displacement near the goaf and the bottom of the isolation layer after the excavation is relatively large.In this case, the slope as a whole will not appear instability, but local damage may occur, The slope and isolation layer need to be protected at the same time. By comparison, it can be seen that the overall safety factor of the filling method is high, Therefore, filling method can be given priority in future mining.

Key words: The open-underground combined mining, Slope, Numerical simulation, Stability analysis