At present, little attention has been paid to the seepage and stability of landslide under different combination of reservoir water level and rainfall. Based on the theory of unsaturated seepage and stability analysis, taking the Caipo accumulation body in the three Gorges Reservoir area as the research objective, the rainfall was analyzed by the Geostudio software. The seepage characteristics and stability of the accumulated slope under the reservoir water level and its combined working conditions were simulated by numerical simulation, and the variation of pore pressure in different parts of the slope, the safety factor curve of the slope and the development law of the wetting front were obtained. The results showed that the larger the drop rate of reservoir water level, the faster the pore pressure decrease, the greater the intensity of rainfall does, the larger the range of pore pressure rise, and the greater the amplitude of pore pressure rise of simple rainfall is greater than that of reservoir water level. The variation characteristics of pore pressure at the time of sudden drop of reservoir water level are combined with rainfall and reservoir water level. The safety coefficient of reservoir water level drops first and then rises. In case of rainfall, the safety coefficient drops first and then remains stable. The amplitude of safety coefficient caused by rainfall is larger than that of reservoir water level drop. Rainfall occurs at different times of reservoir water level. The safety coefficient has a sudden drop at the time of rainfall and arrives at minimum, of which rainfall occurs at the 6th-8th day. The probability of slope instability is the highest when the water level suddenly drops in the combined rainfall reservoir. The water level of reservoir drops more rapidly. The greater the degree of degree, the fuller the progress of the wet front on the surface of the slope. The change law of the wetted front under the action of rainfall and reservoir water level is similar, but the degree of convex of the infiltration line is different, which is the reason for the inconsistent safety factor of the slope in this case.