The combined entrance section of Bosamu reservoirs is at high risk for its high and steep rocks.Based on the strength reduction method,this paper uses the finite element to analyze the stability of the natural working condition and excavation working condition of the slope,and obtains the safety factor and adverse sliding surface.The results show that the plastic zone of the slope starts from the bottom of the slope and extends upward,and local instability has occurred before it reaches full penetration.The safety factors of the two working conditions meet the requirements,but the safety factor of the excavation working condition is small,and the sliding surface is different.Compared the three instability criteria,the calculation misconvergence and displacement mutation are consistent,and the penetration of plastic zone is not applicable in the case of local instability.