Abstract: Mudslide disaster events had occurred in the Dharma Gully sub-basin area historically and caused a large casualties and property losses.At present, a large amount of coal gangue was piled up in the main ditch of the sub-basin, and more landslide deposits were accumulated on both slopes sides of the main ditch.In order to analyze the possibility and risk of mudslides reoccurring, this paper analyzed the development of mudslides in Dharma Gully sub-basin area in detail through UAV photogrammetry and field investigation.Based on the improved MacCormack-TVD finite difference method, the Massflow software was used to simulate the mudslide conditions and obtained the mudslide risk in Dharma Gully under 4 rainfall probabilities of 10years, 20years, 50years, and 100years.The results showed that:(1) Under the above 4 rainfall probabilities, the flow velocity of debris flow in most areas was 0～3 m/s, the mud depth was 0～4 m.The maximum flow rate could reach 19 m/s, and the maximum mud depth could reach 3.85 m;(2) Under the rainfall of 100-year, the high-risk areas in Damogou accounted for 16.54%,the medium-risk areas accounted for 49.27%,and the low-risk areas accounted for 34.19%;(3) The simulation results reproduced the temporal and spatial development characteristics of debris flow well, showed the influence of rainfall intensity on the movement of debris flow, which could provide some references for the early warning and monitoring of debris flow.