Abstract: Rock mass stability on the west out slope of upper reservoir is one of the main geological engineering problems for Ming Tombs Pumping Storage Station. Since there exist several gently dip angle faults which incline to outside of the reservoir and bad rock mass structure, there is possibility of slide displacement and deformation instability, which may potentialy threatene the safe operation of the station. So it is necessary to analyze the rock mass stability on the west out slope and to make engineering reinforce treatment.