Abstract: Based on the digital mine model of Manjiazhai stope， 3DMine software was adopted to optimize the open pit limit to get the mining boundary with different final slope angle. Then， the limit equilibrium analysis was used to analyze the stability of open pit boundary with different slope angles at Manjiazhai stope and to calculate the stability factor of slope. With comparison of the stability index of each program， the income of open-pit mining on the premise of ensuring slope safety can be maximized， so as to find out the balance between the open mining income and the risk of slope. This method may provide reference for the design of the open-pit boundary.

Key words: Open-pit mine, Pit limit optimization, Slope stability, Risk benefit