Abstract:FLAC3D numerical simulation software and strength reduction technique were applied to determine the safety factor of rock slope with soft interlayer in a section of Changde-Zhangjiajie highway. Solution efficiency, stability criterion and other problems are discussed, related with the simulation course. The case study indicates that the convergence criterion combined with the interpenetration of the plastic zone criteria can well simulate the practical project. And the convergence criterion takes the slope failure as the indicator to achieve the automation of loop computation. At the same time, the plastic zone criterion can be used to decide the number of steps in the calculation. The calculated error of the strength reduction method can be made much smaller while combining with dichotomy, and the result tends to be more conservative and more accurate as compared to the limit equilibrium. In addition, the strength reduction method can accelerate the speed of calculation to a great degree, the calculated time for safety factor of 1 and 2 weak interlayers is 2046s and 5929s, respectively. Compared to the calculated time of the strength reduction method inside FLAC3D, the speed of calculation is six times faster, and the safety factor is also more reliable.