Abstract: The Wenchuan "5•12" and Lushan "4•20" earthquakes triggered a large number of secondary disasters in the earthquake area and surrounding areas, providing geological conditions and rich material source conditions for the outbreak of debris flow. Through the research on the earthquake damage of Mozi gully debris flow in G318 Luding section, the analysis of the formation conditions of debris flow, the investigation of disaster history and harmfulness, and the calculation of movement characteristics, the comprehensive treatment measures of "four sand retaining dams + protective dikes and drainage channels" are put forward. Scientific analysis of the formation mechanism and characteristics of post earthquake debris flow, making good use of the situation and following the prevention and control law can better protect the safety of national major traffic trunk lines and people's lives and property, and reduce or even eliminate the harm of debris flow. The investigation and treatment of post earthquake debris flow and the maintenance and repair of existing projects will be a long-term process and the focus of future research.