Taking Zhuziba material-yard slope as an example,it use FLAC 3D to dynamically simulate the excavation process. Numerical calculation is carried out and strength reduction method is used to identify the plastic zone and the potential sliding surface. Sensitivity analysis is carried out to determine the influence on the the values of c and φ of the monitoring points on displacement. And combined with the measured displacements of the point, back analysis is carried out to determine the mechanical parameter of the potential slip surface. Based on analyzing the effect of anchorage on the anchoring method, 2 excavation - supporting schemes are designed. The results show that it can be accepted to identify the potential sliding surface by using strength reduction method, because the result is similar to what is drawn by using stereographic projection. The displacement of monitor point is linear to φ. The influence of φ(c) is similar on displacement at same c(φ).It also can be accepted to determine the best interval of anchor and length of anchoring section of double anchor by using numerical calculation to make the most considerable use of building materials.