Baihetan hydropower power station is located in the lower reaches of Jinsha River. The distance from dam to Qiaojia county of upper reaches is about 45 km. Some areas surround Qiaojia county will be submerged after the impoundment of the hydropower station.The amplitude of water level variation is from 765 to 825 meters.This change may cause slope instability in surround the county area,and produce great impact on people's production and life in the region. After site investigation and through the analysis on composition of formation drill,the paper Analyzed and evaluated the stability of study area before hydropower storage through numerical simulation. The conclusion is that study area before hydropower storage is in a steady state. The result is consistent with the results of the field survey.But earthquake may also produce certain influence on the stability of study area.,so it is necessary to carry on long-term monitoring so as prevent the occurrence of geological disaster.