Abstract: Firstly,the safety factor calculation program is compiled with fish language embedded within FLAC~ 3D for the second development based on the strength reduction method. With a case study, this method is applied to 3D analysis on landslide stability with confirmed sliding zone in this paper. Then computation is completed for its 2D and 3D safety factor in natural condition. At the same time, inversions of friction angle and cohesion parameter are analyzed. Comparison of calculation results with limit equilibrium method and FLAC~ 3D is also analyzed. The results indicates: ①The safety factor computed with strength reduction FLAC~ 3D is a little bigger than limit equilibrium method. ②The calculated result of 3D strength reduction FLAC~ 3D is ratherish larger than 2D because of three dimensional effect. ③The increasing cohesion and internal friction angle results in a increase of the safety factor with different methods, furthermore, the influences to 3D strength reduction FLAC~ 3D is a litter more significant than 2D with the cohesion and internal friction angle. Secondly, simulation is made for the sliding direction under limit equilibrium situation, and the analysis result is obtained as that the entire landslide is basically stable with probably local failure. Finally, influencing factors are discussed when building the FLAC~ 3D model, such as the range of peripheral rock mass and bedrock under sliding zone and the mesh subdivision of the model.