Abstract: Given the context of climate change and rapid urbanization expansion, China is facing an increasing risk of extreme rainstorm and flood disasters. The "7·20" extreme rainstorm disaster in Zhengzhou City of Henan Province, resulted in significant loss of life and property, revealing many problems such as inadequate awareness and preparation for major disasters, weak prevention organizations, and improper emergency response measures. In this paper, the techniques of rainstorm transplantation and flood simulation are employed, and the distributed hydrological model and 2-D hydrodynamic model are utilized to analyze the flood situation in the Futuan River Basin of Rizhao City under the "7·20" extreme rainstorm scenario. The two schemes that the rainstorm center is located in Sanzhuang Town in the upper reaches of the Futuan River and Rizhao street of the downtown area in the lower reaches are proposed. A comparison and analysis of the flood impact of two schemes is provided. According to the findings of this study, both Rizhao Reservoir and Maling Reservoir in the watershed experienced inflow flood peaks that exceeded their historical maximums under the two schemes. The overall disaster area of downstream social-economic zone was 151.96 km² and 166.02 km² respectively. When the center of the rainstorm was situated in the urban area, there was an increase in average submerged depth of the downstream area from 0.46 m to 0.73 m, resulting in a rise of 9.3percent in damage area within the social-economic zone. Under the current engineering conditions, in the event of an extreme rainstorm in the Futuan River of Rizhao City, floods will pose a significant threat to numerous residential areas, critical institutions and infrastructure. Therefore, it is imperative to develop emergency plans and conduct pre-flood drills based on scenario analysis for such extreme rainstorm events.