This paper is based on the rock mass geo-engineering background of the Maocaopo slope. Detail survey reveals some phenomena, including topple, shear, slip and tension. After analyzing the deformation phenomena and monitoring data, the conclusion is that the unstable slope deforming mode shows change characteristics, which change from toppling-tension mode to slipping-tension mode. The impounding and periodic adjustment in the Three Gorges Reservoir results in water fluctuation zone in the foot of the Maocaopo slope. This is not good to the stability of the Maocaopo slope and accelerates the development of the slope.