Abstract: Based on the theory of finite difference strength reduction，numerical simulation was carried out on the stability of the open pit slope using FLAC. Some safety parameters have been reported under mutations of iteration numbers，non-convergence of the calculation，and the plastic zone connection. The result shows that the slope damage can be revealed to be non-convergence of the calculation in the numerical simulation，while the connection of plastic zone is only the necessary condition of the slope damage.

Key words: Open-pit mine, Slope stability, Strength reduction methods, Numerical simulation