Abstract: Many geological disasters such as the debris flow and landslide caused by the rainstorm happened on 8^th, 9^th and 10th of July in Daguangbao-Huangdongzi Gully, Sichuan Province. Based on the field investigation, the formation causes of the debris flow, developing trend and risk assessment are analyzed. The investigation results show that: ①The Daguangbao-Huangdongzi Gully debris flow belongs to the typical Gully Debris flow and could be divided into Formation, Circulation and Deposit area; ② The debris flow formation includes the loose material provided by Daguangbao landslide and the volume is up to 10⁷ m³; extreme rainfall climate directly started the loose deposit to form the debris flow and the geographical conditions is conducive to the erosion, transportation and deposition of debris flow. The debris flow is still in the active stage and will be strengthened in the future; ③The conclusion after the risk assessment shows that the debris flow poses a moderate risk with the fatalness degree of 0.482.