Abstract: Rainstorm and capacity building for disaster prevention are important factors that affect the occurrence of flood disasters and the changes in their losses. Based on the rainstorm-flood disaster data, daily precipitation data observed by meteorological stations, and socio-ecomomic data in the Jiangnan region (Shanghai, Zhejiang, Fujian, Hunan, and Jiangxi) from 1978 to 2018, the spatiotemporal variation characteristics of rainstorms and losses caused by rainstorm-flood disasters were investigated in Jiangnan region in the recent 41 years. Results show that the affected area, the damaged area, the affected rate and the damaged rate of crops by rainstorm-flood disasters show a "first rising-then falling" trend in the recent 41 years in Jiangnan region. A relatively high level period is found in the 1990s. The spatial distribution of disasters shows a characteristic of "more in the west and less in the east". In the past 41 years, the frequency and intensity of rainstorm in Jiangnan region have fluctuated and increased, the duration and spatial concentration are increasing, showing a characteristic of "higher in the middle and east of the Jiangnan region and lower in the west". Rainstorms are concentrated from May to August, especially in June. Except for the number of severe rainstorm days, the number of rainstorm days, the number of extreme rainstorm days, and the accumulated rainfall amount of the rainstorm all are significantly and positively correlated with the sizes of affected areas and injured areas as well as the affected rate of the crops. The increase in the intensity of rainstorms is an important factor that contributes to the increase in the affected area, especially the damaged area. The intensity of heavy rainstorms has increased, which have a positive impact on the area affected by the disasters, especially the increase in the area damaged by the disasters. The consecutive rainstorm days, the standard deviation of rainstorm days per month, and the standard deviation of the rainstorm days per station are significantly and positively correlated with the affected area, the damaged area, the affected rate, and the damaged rate, indicating the stronger the spatiotemporal concentration and the sustainability of rainstorms, the greater the disaster loss. There are decadal differences in the relationship between precipitation and disaster losses, and the correlation between them has shown a decreasing trend in recent years. The frequency and intensity of rainstorms are not completely consistent with the distribution of flood-induced losses in time and space, indicating that the occurrence and impact of rainstorm-flood disasters are not only affected by meteorological factors, but also by disaster-bearers and social factors. The construction of disaster prevention in the Jiangnan region is spatially characterized by "strong in the east and weak in the west". The ability of disaster prevention in Jiangnan region has gradually developed, which has played an important role in reducing disaster occurrences and disaster losses. Therefore, in the Jiangnan region, especially the western Jiangnan region, disaster prevention should be further addressed.