Abstract: The stability of slopes under complex geological conditions is obviously affected by factors such as structural plane and rock mass properties, and its accurate evaluation is very important for the safety of slope construction. Based on the construction project of the inlet slope of the diversion tunnel of the Cihaxia of the Yellow River, this paper proposes a comprehensive evaluation method of slope stability based on the stereographic projection theory, the two-dimensional limit equilibrium and the three-dimensional limit equilibrium method.Firstly, based on the stereographic projection theory, the unstable block of slope 4# toppling body with complex structural plane is qualitatively described. Then, the two-dimensional limit equilibrium and three-dimensional limit equilibrium methods are used to analyze the risk of slope instability induced by layer-by-layer excavation during construction. Finally, from the perspective of multi-method comprehensive evaluation and cyclic optimization, a targeted support optimization scheme is proposed according to the design principle of ’ less excavation +strong support ’, and the optimization scheme is evaluated from the perspective of safety and economy. The calculation results show that the slope stability safety factor of the large excavation scheme is about 1.17～1.19, and the safety factor of the small excavation scheme is about 1.078. The slope safety of the large excavation scheme is higher than that of the small excavation scheme. After the support optimization of the small excavation scheme, the safety factor of the slope stability increased to 1.159～1.183, the slope stability changed from critical stability to stability, and the support optimization effect is remarkable. Based on the safety and economic evaluation of slope excavation, it can be seen that the proposed ’ less excavation + strong support ’ optimization scheme meets the safety control standards of slope excavation related specifications, and has good economic benefits and engineering value, which can provide reference for related projects.