Debris flow at a rainfall frequency of 2% was triggered by rainstorm on July 10, 2013 in Miansi town, Wenchuan County, Sichuan Province, blocking Minjiang River and endangering the settled population downstream area. Based on the 1∶[KG-*3]10000 contour, rainfall data and remote sensing image of 2013 and the flied investigation in Cutou gully, FLO-2D software is used to simulate the movement and accumulation process of debris flow under different rainfall frequency (5%, 2% and 1%) for studying the hazard of debris flow in Cutou gully. Under the condition of 2% rainfall frequency（the actual rainfall frequency）, the simulated maximum debris flow velocity is 12.99m/s and the maximum debris flow mud depth is 15.7m, and the accumulation area is 9.55 ×104 m2. Verified by the actual accumulation zone，the accuracy rate was 77%. The simulation results are in a reasonable error range and show high reliability. The strength model of debris flow was created through the mud depth and flow velocity. In addition, the debris flow hazard assessment model is constructed by combining the strength of debris flow and the return period of the outbreak. In this way, the risk assessment of debris flow in Cutou gully is realized and the distribution map of hazard zone in fan area is obtained, where the high dangerous area accounts for 61%, the moderate dangerous area accounts for 19%, and the low risk area accounts for 20%. It provides a scientific reference for prevention and control of Cutou gully debris flow.