Abstract: On July 26, 2016, a heavy rainfall suddenly happened in Wolong County, Sichuan Province, which caused mountain torrents across the Wolong territory of Pitiao River tributary, inducing debris flow disaster. Based on environmental geologic conditions, especially characteristics of the source conditions under heavy rainfall condition, the authors discussed the starting and accumulating process and disaster characteristics of Xiongmaogou debris flow. The results showed that heavy rainfall was the dynamic factor for debris flow to occur; the disaster scale was large, which poured about 50million cubic meters earthwork; since no debris flow protection engineering was built in the channel, and the flood control facilities construction standards was low, the flood control dam was filled with mud and the fluid overflowed the river and rushed to the downstream houses, resulting in serious disasters. The typical example of Xiongmaogou debris flow indicated that debris flow in Wenchuan earthquake area has become active. Therefore, it's necessary to carry out debris flow risk assessment and monitoring and disaster early warning in Wenchuan earthquake area, and to take effective engineering measures to control the occurrence of debris flow to reduce the damage.