Abstract: A large number of collapse and landslides triggered by Wenchuan earthquake. Massive loose material is formed.it created the basic conditions for the formation of debris flow. The formation of the dam-breaking debris flows are special.the dam-breaking debris flows has the character of big-scale, sudden outbreak, short duration, strong erosion carrying ability. It often cause serious harm.this paper taken the Qipangou dam-breaking debris flow in Wenchuan area as an example. Basic on the analysis of the debris flow formation conditions and detailed description about the basic characteristics of the collapse, the paper analyzed emphatically the multistage dam-breaking process.it can provide reference for further understanding the formation of dam-breaking debris flows after earthquak, parameter selection and prevention and control measures.