Abstract: In order to prevent, respond to, and reduce the mass death and injury caused by rainfall-induced torrential flood and debris flow disasters more effectively, the author carried out the cause analysis of the disasters based on empirical cases.By describing the basic and hazard characteristics of mountain torrential floods, debris flows and torrential flood-debris flow disasters, the disaster factors are analyzed that consists of heavy rainfall, watershed topography, environmental effects of movement path and disaster bearing body.Torrential flood is divided into suspended load and bed load mountain floods, torrential flood-debris flow is divided into mountain debris flows and mountain flood rock flows, and debris flow is divided into mud flows and debris flows to serve in identifying the cause and nature of the disasters.