[Objective] To provide reference for disaster prevention and control of river-blocking debris flow of Haermu gully in Wenchuan area after earthquake.[Methods] By in-situ investigation

the changes of geological environment was analyzed systematically based on the formation of debris flows after Wenchuan Earthquake. The possible size of the debris flow under different rain frequencies was studied. We used four experience formulae to evaluate the risk of debris flow.[Results] The characteristics of debris flow

confluence condition and hydrologic condition of main river were conducive to debris flow blocking the river. Calculated by the 4 empirical equations

it was indicated that there was risk of river blocking when P=1% and above. After the comprehensive treatment for 7 debris flows within 3 years

significant improvement have been achieved. However

issues such as project layout unreasonable

abutment seepage

overflow port siltation

erosion damage to drainage canal still existed.[Conclusion] To solve those issues

we suggested that more check dams need to be built and drainage canal need to be reinforced in the future.