[Objective] To meet the demands of constructing a modern reservoir operation and management matrix and to further enhance the flood forecasting and early warning capabilities of the Danjiangkou Reservoir, this study simulates the over-standard flood discharge scenario of the Danjiangkou Reservoir, and analyzes the evolution and inundated conditions of the downstream flood, aiming to improve the accuracy of the flood forecasting visualization and emergency planning. In doing so, the study seeks to provide stronger support for ensuring the safety of the Danjiangkou Reservoir Project and the security of water supply. [Methods] Based on the principles of the continuity equation and the momentum equation, the MIKE series model software was used to establish a two-dimensional hydrodynamic model of the downstream river channel and floodplain. Fully considering the impact of flood evolution on key cities downstream, a computational grid was constructed based on DEM and measured terrain to simulate the flood evolution of the downstream areas during over-standard discharge from the Danjiangkou Reservoir under seven scenarios. The arrival time of flood and peak flood in downstream areas under different scenarios was analyzed. The relationships between peak flood water level, peak flood discharge, design water level, and maximum allowable flow at typical cross-sections were compared. Based on GIS software, the inundation range and inundation depth in the downstream areas under different scenarios were analyzed. [Results] Under the regulation and storage effect of the project, the flood reached Xiangyang and its upstream areas within 2 to 10 hours, the Yicheng-Shayang cross-section within 10 to 24 hours, and the Xiantao area approximately two days later. The arrival time of the flood peak at each typical cross-section exceeded 68 hours. Under the condition of concrete dam failure, the flood spread pattern in the mountainous areas near the dam was similar to that under the regulation and storage scenario, while the flood evolution speed in the plain areas was generally more than 3 hours slower than that under the engineering regulation and control scenario. In the case of sudden over-standard water inflow and earth dam failure, the flood and flood peak in the areas upstream of Zhongxiang arrived within 12 and 18 hours, respectively, while in the areas downstream of Zhongxiang, they arrived after 13 and 31 hours, respectively. There were high risks of embankment overflow in the section from Danjiang to Yicheng. Under the conditions of verification flood, design flood, dead water level failure of the concrete dam, and failure of the elevated part of the concrete dam, the inundation depth of most areas from the dam site to Fancheng, Xiangyang was 16-20 meters, while that downstream of Tianmen was less than 3 meters. In the case of a severe flood in which all soil and rocks collapsed, the inundation depth from the dam site to Fancheng, Xiangyang was approximately 35 meters, while that of the Danjiangkou section exceeded 50 meters. The flood in Shayang County caused the inundation of over 70% of the area in Qianjiang City, with the overall inundation depth below 2 meters. [Conclusion] Based on the above results, this study provides strong support for the emergency preparedness for the safety management of the Danjiangkou Reservoir Dam, the development of a visualized flood rehearsal, and the construction of a modern reservoir operation management matrix.