The stability evaluation of high rock slope is one of key issues during construction period. A unitary evaluation method is inadequate and incomplete. The stability of left bank slope of Jinping First Stage Hydropower Station is very outstanding because of its complicated geological conditions. The deformation mechanism and slide modes of left bank slope were analyzed and the safety factor of each mode was calculated. The stability of left bank slope during construction period was evaluated synthetically by using various safety monitored results and those results with several typical unstable rock slopes were compared. Research result shows that the left bank slope is stable basically and support measures can satisfy the stability requirement and some suggestions on safety monitoring were given.