Abstract: Heavy rainfall is a major causes of sedimentary landslide disasters, and understanding the spatiotemporal dynamic characteristics of the seepage field in landslides under heavy rain is crucial for evaluating landslide stability and providing meteorological risk early warnings. Current simulations and analyses often focus primarily on rainfall intensity as the change parameter, which limits their effectiveness. This study takes the No. Ⅲ landslide of Sankeng Village Landslide Group in Fengshun County, a super-large geological disaster in Guangdong Province, as a case study. Based on the field investigation and data analysis, a refined landslide geological structure model was developed and statistical methods were used to analyze the rainfall characteristics in the area, classifying the rainfall into “uniform type” and “peak type”. The dynamics of the seepage field under these two types of rainstorms was analyzed by simulating changes in the infiltration line and pore water pressure within the landslide. The stress-strain field and displacement characteristics of the landslide were then examined, and stability was quantitatively evaluated. The results show that the uniform rainstorm will significantly affect the seepage field in the deep part of the landslide, resulting in noticeable local deformation. The landslide response to peak rainfall varies with the change of position, with forward rainfall causing traction-like deformation, while backward-moving peak rainfall induces a pushing deformation. The numerical simulation results align well with the observed deformation of the landslide. This study can provide basic information for the design of the treatment and protection engineering of the accumulation layer landslide.