Abstract: From June 10 to 13, 2019, continuous heavy rainfall occurred in Longchuan County, resulting in a large number of landslides and debris flows in the county. Mibei village is one of the three hardest hit areas. Taking the landslide debris flow chain disaster in Mibei village No.6 gully of Beiling town as the research object, this paper studies the characteristics and disaster mechanism of chain disaster on the basis of field fine investigation and measurement, combined with numerical simulation analysis and calculation. It is found that: ①there are 7 soil landslides in the No.6 gully. Only NO.3 landslide mass and part of NO.6 landslide mass are transformed into debris flow, which constitutes the main material source of debris flow, and the other landslides do not constitute a sustainable impact; ②With continuous rainfall infiltration, the slope body changes from unsaturated to saturated state, and a continuous saturated zone is formed on the slope surface. The increase of pore water pressure and the softening of pore water reduce the strength of soil. In addition, the increase of saturated weight of slope body leads to the instability and failure of shallow surface layer of slope; ③The continuous infiltration of rainfall and the surface catchment under the "funnel" terrain of the branch gully source rapidly increase the water content in the loose accumulation of the landslide, promote the change of its physical properties, start and move in a flow state under the gravitational potential energy, and transform it into debris flow. The rainfall structure affects the chain process of landslide debris flow. The landslide is caused by early rainfall and the debris flow is formed by later rainfall. The occurrence of landslide and debris flow shows phased characteristics. The research results are helpful to guide the local government to further carry out the disaster prevention and reduction of landslide debris flow chain disasters, and also provide theoretical support for the future regional early warning research in this area.