The frequent recurrence of climatic extreme events and the sharp increase in the frequency and intensity of precipitation have increased the risk of coastal flooding. To reduce regional flood risks, we analyzed the formation mechanism of flood risk in four dimensions: risk of contributing factors, sensitivity of breeding environment, vulnerability of hazard-bearing bodies and disaster prevention and mitigation capacity. Based on 11 indicies, the ArcGIS and entropy method were used to evaluate the flood risks in Hunan section of the Xiangjiang River Basin, then the final flood risk map was produced at the district and county scale. The results show that the risk of contributing factors is low in the central and western parts of the Xiangjiang River Basin, while the sensitivity of breeding environment in the central part is high; the vulnerability of hazard-bearing bodies is relatively high in the Changzhutan Rim and Hengyang City, but the former has a relatively high disaster prevention and mitigation capacity due to its good economic foundation; the distribution of flood risk in the Xiangjiang River Basin increases from northeast to southwest, with high flood risk areas in Changsha City, Yiyang City, Hengyang City and southern Yongzhou City. The different dominant factors in different regions reflect the differences in flood risks under the effect of multiple factors, the research results can provide a technical support for regional flood prevention and mitigation.