Abstract: This paper establishes the FLAC computation simplified model for the rock slopes in the north side of Gongchangling Open Pit.It simulates and analyzes the longitudinal fault by adopting the weakening method and the interface method.In the numerical simulation，Mohr-Coulomb model with 10 steps is adopted in mining to analyze the discontinuous of stress and displacement in the rock affected by faults.Then，the evolution law of the surface slope rock，the fills in faults and fracture zone，and rock plastic flowed area，plastic unloading area and tensile failure zone near the faults are confirmed.The adaptive feature of mechanical behavior of faults by the two methods and their merits and demerits are compared and analyzed.

Key words: Longitudinal fault, Weakening method, Interface method, FLAC