Abstract: The Anning river basin is a densely distributed area of geological hazards, where the Anning river rift crosses, with complex tectonics and the Lengzi gully developing in the upper left bank. The gully is subject to mudslides under heavy rainfall conditions, blocking the Anning river basin and burying houses and roads in the village of Yema. Lengzi gully debris flow has the characteristics of small area,a short main trench and a large channel longitudinal slope. To explore these damage, taking Lengzi gully as an example, the intensity of debris flow burst under different rainfall cycles is analyzed, and the movement process of debris flow is simulated and the risk assessment is carried out. Combined with the simulated maximum flow velocity, maximum accumulation depth and rainfall intensity,the hazard assessment model is established.The results show that in the danger range of Lengzi gully debris flow, the high risk area accounts for 27%, mainly distributed in the channel with more loose solid materials, and the medium risk area and low risk area account for 56% and 17%, respectively. this conclusion provides a scientific basis for the monitoring and early warning of key facilities in the danger range.