The Mozi gully, located in Yinxing, Wenchuan County of Sichuan province, is a tributary of Minjiang River at the right bank. This gully was seriously affected by the Wenchuan earthquake on May 12, 2008. Numerous collapses and landslides triggered by the earthquake provided abundant materials for debris flow, and eight of them blocked Mozi gully. Debris flows had occurred many times in this gully from  July to September in 2008 and 2010, and blocked the Minjiang River  for 3 times and inundated  villages on the left bank. Similar situations happened in 2009, 2010 and 2011. According to field investigation and interpretation of remote sensing images and aerial images in different periods, there are more than 3 000×104 m3 solid loose materials in Mozi gully after the earthquake. According to debris flows in different rainstorm frequencies, the biggest debris flow on  July 14, 2008 is calculated to be 257 000 m3, with a peak discharge of 541 m3/s, once in half a century. The sediment volume carried out from the gully is only 2.5×106 m3, and the left materials are still of high risk of triggering debris flows and blocking the Minjiang River.