Abstract: The identification of slope geological disaster risk has become an important basic work for geological disaster prevention and control in southwest mountainous areas. The potential unstable slope units are divided by GIS program, and six factors including dip angle, elevation, thickness of covering, slope soil type、human engineering activities and maximum rainfall were selected as evaluation factors. Analytic hierarchy process (AHP) is carried out to assess risk of large-scale geological hazards in mountainous areas and preliminarily evaluate the unstable slopes in the study area. While taking slope models in study area of Wanshan as examples, the safety factors under heavy rain condition are analyzed with FEM approaches. In this method, we only reduce the strength parameters of elements whose shear strain is beyond the limit value．The reduction process will continue until the global slope failure associated with the formation of whole sliding surface whose limit shear strains beyond the limit value．It is found that all of the safety factors in 12 slopes are below 1.05 which accorded with the results of AHP. It is proved that proposed method can be seen as a quantitative evaluation method for geological hazard identification of the soil unstable slope in southwest mountainous area.