Abstract: At present, a certain gold mine adopts open-pit mining for production, and a 400 m ultra-high slope has been formed in the northwest. The main transportation road in the northwest, as a permanent road, has high requirements for slope safety. Due to the influence of longitudinal extension mining, it is necessary to conduct research on slope safety at this stage. This article focused on the actual exposed status of slopes, and based on on-site surveys and relevant laboratory experiments, it obtained the structural plane and attitude of the northwest slope, as well as the mechanical parameters of the rock mass. By using the stereographic projection method and limit equilibrium analysis method as research methods, the stability of the slope was analyzed. The results show that the stereographic projection method can analyze the formation of wedge-shaped shapes between joints and slopes, and there are many potential sliding surfaces. The local potential failure mode is wedge-shaped failure. The limit equilibrium method analysis finds that as the longitudinal mining continues, the safety factor of the northwest open-pit slope is less than 1.0 due to the influence of self weight, groundwater, and earthquake. The contact fault position of the main transportation road on the slope is prone to instability and damage, which has a certain impact on the main transportation road. Continuous attention should be paid to the safety and stability of this location. The research results provide theoretical basis for mine design and production.