According to the survey and study on geological condition, the genetic mechanism and evolving process of the reservoir landslide were analyzed at first that the landslide experienced two large slides. The first slide occurred in the J2S2 formation, it's a collapse slide with small thickness sliding mass, but made the slope on the back edge of the landslide became steeper, which created the conditions for the second slide. The second slide mainly occurred in the J2S1 formation, it's a slide that cut layer of rock stratum, which formed present landside. Then, the influencing factors on the stability of reservoir landslide were analyzed, and finite element models were created to calculate and analyze the stability of reservoir landslide under multiple-factors action. The results shows that the landslide is stable in natural conditions, and the safety factor of landslide decreases after the normal storage of reservoir, which doesn't meet the specification requirements; when considering the sudden drop in reservoir level, rainfall infiltration and other factors, the safety factor of landslide decreases further, reaching the critical stable state, and landslides may be unstable when considering earthquake. Therefore, cutting slope and reducing load were suggested, and the calculations show that the landslide trends toward stable under action of multiple-factors after treatment, which means the research achievement has a great reference value to guide engineering design and construction.