[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.