[Objective] The dam failure of upstream reservoirs in urban areas poses a serious threat to the safety of people's lives and property. Analyzing the simulation process of flood evolution caused by reservoir dam failure in urban areas to provide scientific basis for reservoir dam failure risk prevention, early warning system development, and evacuation plans. [Methods] Taking the upstream Jiangang and Changzhuang reservoirs in Zhengzhou City as examples, a high simulation terrain digital elevation model is constructed based on GIS technology. The MIKE FLOOD coupling model is used to couple the one-dimensional and two-dimensional models of reservoir dam failure, simulate the flood evolution process after reservoir dam failure, and explore the evolution characteristics of floods in downstream rivers and complex urban areas. [Results] Immediately upon reservoir dam failure, peak discharge at the breach quickly reached its maximum. Peak outflow volumes from Changzhuang and Jiangan reservoirs were 4542.03 m3/s and 17549.1 m3/s, respectively, with non-converging flood peaks. Portions of both banks downstream of Jialu River within 15.00 to 31.39 km from Jiangan reservoir were inundated, covering an area of 56.37 km2. One hour after Changzhuang reservoir breach, river banks began to overflow, resulting in inundation areas. Jiangan reservoir dam failure occurred 4.25 hours later. 1.25 hours after Jiangan reservoir breach, inundation depths significantly increased in the original inundation area, expanding further to maximum inundation area 1.92 hours later. After the dam break of Changzhuang and Jiangan reservoirs, the flood water level increased to more than the top of the South-to-North Water Transfer Protection Embankment, and a large amount of flood surged into the main channel of the South-to-North Water Transfer, and the flood flow rate generally increased. [Conclusion] The flood peak flow of Jiangang Reservoir is significantly larger than that of Changzhuang Reservoir, and the dam break is more harmful. After the dam break, a large amount of flood flows into the main channel of South-to-North Water Diversion Project, and the risk of erosion of dikes, slopes and inlet and outlet lock chambers increases. It seriously affects the water conveyance safety of the main canal of the South-to-North Water Diversion Project and the safety of people 's lives and property.