Display omitted •This study included one million RTI cases during 2006–2021 across China.•We projected the heatwave-related RTI at provincial and national level until 2090s.•Compared with non-heatwaves, the risks of RTI increase by 3.61% during heatwaves.•Modifications by age, occupations, mechanisms of RTI, and regions were observed.•The heatwave-related RTI will substantially increase in the future. Previous studies have demonstrated health impacts of climate change, but evidence on heatwaves’ associations with road traffic injury (RTI) is limited. In this study, individual information of RTI cases in May-September during 2006–2021 in China were obtained from the National Injury Surveillance System. Daily maximum temperatures (TMmax) during 2006–2021 were collected from the ERA-5 reanalysis, and the projected daily TMmax during 2020–2099 were obtained from the latest Coupled Model Intercomparison Project Phase 6 Shared Socioeconomic Pathways scenarios (SSPs). We used a time-stratified case-crossover analysis to investigate the association between short-term exposure (lag01 days) to heatwaves (exceeding the 92.5th percentile of daily TMmax for ≥ three consecutive days) and RTI, and to project heatwave-related RTI until 2099 across China. Finally, a total of 1 031 082 RTI cases were included in the analyses. Compared with non-heatwaves, the risks of RTI increased by 3.61 % during heatwaves. Greater associations were found in people aged 15–64 years, in people with transportation occupation, for non-motor traffic vehicle injuries, for severe RTI cases, and in Western China particularly in Qinghai province. We projected substantial increases in attributable fraction (AF) of heatwave-related RTI in the future, particularly in Western and Southwest China. The national average increase in AF (per decade) during 2020s-2090s was 0.036 % for SSP1-2.6 scenario, and 0.267 % for SSP5-8.5 scenario. This study provided evidence on the associations of heatwaves with RTI, and the heatwave-related RTI will substantially increase in the future.