Abstract: The FLAC^3D modeling,under complex geologic condition,is brought to success by coupling ANSYS with AutoCAD and Surfer by VC or Fish-Language programming.Based on the trial statistical datum,geological investigation and Hoek-Brown rock mass strength estimation method,the rock mass strengths are decided.And then the numerical calculations of mechanical distortion are finished under the two different instances,namely without taking account of groundwater and 3D fluid and stress coupling analysis.By comparative analyzing the distribution of ground displacement field,principal stresse field and plastic zones under the two different instances,and slope safety factor get by shear strength reduction method without taking account of groundwater.The analysis results show that the potential failure model of combined body of open pit slope and external dump slope is complex,and the slope may be instable under the influence of groundwater.The paper concludes that the superiority of 3D numerical analysis in the analysis of slope stability is obvious,which deserves practice and generalization.