September 15, 2016 8:00 to September 17, 2016 8:00，continuous heavy rainfall led to the territory of Yuanmou occurred more debris flow disaster,in particular, at 9:00 on September 17, 2016, there was a large debris flow disaster in Hailuo Village and Zhubu Village,Huangguayuan Town and causing serious losses.Based on the analysis of the characteristics and formation mechanism of debris flow in Leinong gully，which can be used as a reference for predicting the debris flow in the future and provide a basis for debris flow control and prevention.Analysis and summary of the“9·17” debris flow disaster formation conditions and characteristics,the causes of “9·17”debris flows are researched in three aspects of rainfall condition，topographic condition , source condition and so on. The analysis results show that the abundant prophase rainfall，high rainfall and short duration rainfall intensity provides favorable rainfall conditions. The abundant prophase rainfall can greatly weaken the strength of rock soil mass;The slope gradient and gully bed gradient of most debris flow gullies belong to the scope of prone range in Dongshan aera.The topography conditions are favorable for the formation of debris flow.The material sources for debris flows are rich in Dongshan district.The result indicates that the material sources are mainly concentrated in the regional fracture and human activity area Which provided the necessary conditions for the debris flow in gully. In a word，the “9·17” rainstorm-induced debris flow disaster was the product of the combined action of favorable topography，material source conditions and high-intensity rainstorm.