Abstract: With the rapid development of engineering construction in mountainous areas, the stability of high slopes containing adverse geological conditions such as fault fracture zones has become increasingly prominent, posing a key challenge to project safety and efficiency. This study focuses on a slope engineering project containing fault fracture zones. Using the FLAC3D numerical simulation software, a three-dimensional slope excavation model was established. Through step-by-step excavation simulation and the strength reduction method, the evolution patterns of the stress field, displacement field, shear strain increment, and safety factor during the excavation process were systematically analyzed. The results indicate that as excavation proceeds, slope displacement gradually increases, with total displacement rising slowly from 4.30 mm in Stage 1 to 16.1 mm in Stage 5, and ultimately surging to 334 mm during catastrophic instability. The tensile stress zones expand toward the slope crest, shoulder, and fault zones, while the safety factor continuously declines from an initial value of 1.63 to 1.13 before over-excavation. Ultimately, during the over-excavation stage, a continuous sliding surface forms, leading to circular shear failure. The deformation and failure process of the slope can be summarized into four stages: "unloading deformation – tensile deformation – compression-bending deformation – shear failure." The presence of fault fracture zones significantly reduces slope stability, and over-excavation further exacerbates the risk of instability. The findings of this study can provide important references for the design and construction of slope engineering under similar geological conditions, as well as for subsequent related research.