Wenjia gully is located at the epicenter area of the 2008 Wenchuan Earthquake. A huge landslide was ever triggered by the earthquake. In this paper, on the basis of tracking investigation, the mechanism and characteristics of the Wenjia-gully debris flows were discussed and some suggestions were put forward. The acknowledges are as follows: 1) the debris flows were caused by both Wenchuan earthquake and strong rainfall; 2) the critical rainfall initiated debris flow was significantly decreased and a power-law relation is existed between debris flow magnitude and daily rainfall; 3) as the occurrence process is concerned, the debris flow lasted for a long duration and moved a far distance; 4) in terms of destroying process, a clear chain characteristic was taken on with several damage ways; and 5) Debris flow magnitude was enlarged and the frequency was higher obviously.