Based on the downscaling simulations of 14 global climate models from CMIP6, the spatiotemporal changes and population exposure degree in successive flood-heatwave extreme(SFHE) events in China under the SSP12.6, SSP24.5, and SSP58.5 scenarios were projected. The relative effects of climate and population and their combined effects on the population exposure degree were quantified. The results indicate that climate warming exacerbates the risk of SFHE events in eastern and southern China in the future, and leads to the increases in the duration and land exposure degree of SFHE events. Overall, by the end of the 21st century, under the SSP12.6, SSP24.5, and SSP58.5 scenarios, the annual average frequency of SFHE events in China is expected to increase by 0.13, 0.28, and 0.44 times, respectively, relative to baseline period from 1961 to 2014. The average duration of SFHE events is expected to increase by 1.4, 3.9, and 8.1 d, respectively, the annual land exposure degree is expected to increase by 6.0%, 13.8%, and 18.3%, respectively, while the average interval between flood and heatwave is expected to decrease by 0.16, 0.37, and 0.75 d, respectively, indicating a stronger suddenness of SFHE events. The areas with a significant increase of the population exposure degree are mainly concentrated in eastern and southern China, and the effect of climate change on the increase of population exposure degree is gradually strengthening over time.