The magnitude and frequency of mountain hazards will continue to increase because of climate change especially in rural mountainous areas, which have not received much attention. In this article, a debris flow disaster chain in Southwest China caused damage to buildings along the river bank was investigated. The disaster chain included a debris flow, river blockage, lake formation, and an outbreak flood, and this study further investigated the disaster-related losses in downstream villages. Based on the characteristics of failed buildings, three structural types were identified, while the functions of undamaged buildings were affected by flooding or siltation by sediments. In addition, the building layout and riparian vegetation zone influenced the blockage effect, which resisted the flood impact and provided protection to rear buildings. Moreover, this disaster changed the river topography, the studied reach changed from a V shape to a wide-shallow shape, the appreciably affected river length was 6270 m, and the gully bed was noticeably raised 15-20 m. Furthermore, the flood control standard of a 50-year return period was recommended for reference, despite the limitations of these suggestions, we hope that this study attracts the attention of researchers on disaster prevention and mitigation in remote rural areas.