[Objective] The formation mechanism of the group flash flood/debris flow disasters in Ganluo County of Sichuan Province in 2019 was analyzed in order to provide a reference for the prevention and mitigation of flash flood/debris flow disasters in mountainous areas.[Methods] Based on the field investigation of the group flash flood/debris flow disasters in Ganluo County in 2019, combined with relevant images and rainfall data, the influencing factors and formation mechanism of flash flood/debris flow disasters were analyzed.[Results] The flash flood/debris flow disasters in Ganluo County were mainly caused by short-term heavy rainfall, in addition, there were abundant solid resources and favorable landform conditions in the area. The flash flood/debris flow disasters were the production of the interaction between flood and solid materials. The flash flood/debris flow movement was affected by terrain and some engineering facilities. Meanwhile, the flash flood/debris flow squeezed the main channel or even blocked the channel, thus leading to more disasters.[Conclusion] Based on the formation mechanism and disaster-causing characteristics of flash flood/debris flow disasters in Ganluo County, the disaster control measures shuld be based on strengthening ecological restoration and soil and water conservation in disaster-stricken areas, and combining engineering prevention and ecological control.