As the mining industry developed significantly in the last decades and the depth of open-pit mining has increased, the stability of large open-pit slopes has become a major problem directly related to the safety production and development of a mine. However, the overall slope is indeed safer than the local slope based on the existing stability estimation methods. So the existing methods of directly analyzing the stability of the overall slope will produce some errors in the calculation results of the safety factor, and cannot comprehensively reflect the stability of the mine slope. Based on these problems, this paper adopted the idea of gradual analysis and the precise determination of discontinuity properties to perform a limit equilibrium analysis for the evaluation of mine slope stability. A case study slope, referred to as Yangtaowu Slope in Dexing Copper Mine, was selected for the demonstration of the accuracy of this approach. The results indicate that the adopted method can accurately reflect the actual stability of the slope, especially when the mine slope is near the critical state of stability.