Abstract: Rainstorm is one of the most important factors for inducing landslide, but researches on the response mechanism of landslide deformation under the action of torrential rain are still insufficient. In view of this situation, Baijiabao landslide in the Three Gorges Reservoir area is taken as an example, to analyze the deformation response characteristics under the circumstance of rainstorm on the basis of detailed monitoring data. A landslide mutual information method is used to reveal the influences of rainfall and reservoir water level variation on the deformation of Baijiabao landslide under rainstorm conditions. The deformation of Baijiabao landslide is mainly affected by the variation of reservoir water level, and the expansion of slope surface cracks is mainly triggered by rainfall. Rainstorm is the main cause of the accelerated deformation of landslide after rain and rapid expansion of slope surface cracks located in the boundaries. The research method in this paper can be extended to the analysis of the response characteristics of landslide under the combined action of other multi-conditions and provide some references for disaster prevention and mitigation of the reservoir landslides under the similar effect of rainstorm conditions.