[Objective] Extremely heavy rainfall in a short time can induce extremely low frequency debris flow in mountain area, which brings serious threat to human security and ecological environment in mountain area. In this paper, the characteristics and causes of the 2023“8.11” Jiwozi flash flood and debris flow are analyzed, and its risk is evaluated. [Methods] The formation process of the “8.11” 2023 Jiwozi flash flood and debris flow was retrieved by means of field investigation, numerical simulation and actual precipitation frequency. [Results] The results are as follows: (1) The rapid confluence of extremely short duration and strong rainfall resulted in a flood, which resulted in the erosion of loose materials in the gully, formed the effect of “Fire hose”, and caused a small-scale collapse of the mountain, flash flood debris flow is formed in the gully, and the gully is eroded by the help of steep terrain. (2) Under the actual rainfall frequency, the final depth of debris flow is between 0.04 m and 5.63 m, the maximum velocity is 7.43 m/s, and the one-time discharge is 78271 m3. (3) Based on the velocity of flow, depth of mud and hazard range, three high, middle and low risk areas are given, and the high terrain area on the west side of the accumulation fan is the low risk area, which accounts for about 10% of the accumulation fan area, the middle area and the area from the edge of the pile to the road are medium-risk areas, accounting for 62% of the area, while the areas of the south-east and south-west of the pile fan are high-risk areas, accounting for 28% of the area. The research results can provide scientific reference for the risk control of extremely low frequency flash floods and debris flows in the mountainous areas of Qinling Mountains. [Conclusion] The 2023“8.11” Jiwozi flash flood and debris flow is a typical low-frequency flash flood and debris flow disaster induced by extremely short-term heavy rainfall, and the FLO-2D model effectively simulates the movement and sedimentation process of the debris flow, and determines the danger range of the debris flow. The research results can provide a reference for disaster prevention and mitigation of similar low-frequency debris flows in Qinling Mountains.