Abstract: Landslide/debris flow, dammed barrier lake, and subsequent dam-break floods constitute the most frequent geological disasters in mountainous regions, with heavy rainfall serving as the critical inducing factor. In 2020, artificial rainfall field tests were carried out on the residual slope of a debris flow in Hexiluo gully, Ganluo County, Sichuan Province. The study investigated the impact of rainfall on slope stability through analysis of variations in soil moisture content, pore water pressure under heavy rainfall, and X-ray energy dispersive spectroscopy (EDS) test results. Results indicate that pore water pressure and soil moisture content increase significantly during rainfall. As rainfall persists, the extent of slope erosion and failure widens. Concurrently, soil moisture content and pore water pressure increase during slope failure, with consistent patterns observed in both parameters. The result of EDS tests reveal the presence of illite and kaolinite clay minerals in slope soil. Rainfall induces surface soil expansion and softening, reduces soil particle cohesion, causes tension cracks on the slope surface, weakens slope stability, and ultimately leads to erosion and failure. The research results contribute theoretically to understanding the patterns of slope erosion and failure induced by rainfall.