Climate change has caused an increase in extreme rainfall and snowfall in many parts of the world. For example, in the Three Gorges Reservoir area, annual precipitation has gradually increased and the occurrence of heavy precipitation events has become more frequent. As the reservoir water level rises in October, the high water combined with heavy precipitation creates a “special hydrological environment,” which recently caused the Yanguan landslide. The Yanguan landslide is a large-scale soil landslide that has undergone two slides, pushed the Yanguan Road Bridge into the reservoir, and caused serious damage to roads and buildings. In the present study, the combined effects of high water and heavy precipitation on landslide deformation characteristics (movement patterns and evolution processes) have been analyzed and a stability evaluation was conducted through a field investigation and numerical simulation. To comparatively analyze these combined effects of high water and heavy precipitation, a two-dimensional finite element model was created, and four cases of the hydrological environment were calculated with the model. Results show that the factor of safety was maintained in the range of 1.013 to 1.059 before the precipitation conditions changed. However, as heavy precipitation increased in October 2017 (reaching 356.4 mm in 1 month), this “special hydrological environment” potentially decreased the FoS to 0.948, which is 9.6% lower than that observed under normal conditions, and helped drive the Yanguan landslide activity. The analysis of these various combined effects can also indicate the impacts of climate change on landslides in other areas of the Three Gorges Reservoir.