Global warming threatens food security through causing increasing and severe yield losses from heat extremes, especially for smallholder rice-cropping farmers in Asia. Weather index insurance (WII) could transfer weather-related risks, secure farms’ income, and recover agricultural systems. Under future warming scenarios, however, the related studies are still scarce. Here, compared with the historical period (1961-2010), heat-induced loss will approximately increase by up to 5%, 18%, and 26% at 2100 under three shared socioeconomic pathways of CMIP6, respectively. As an ex-ante strategy, county-specific WII will improve farmers’ income by up to 13% and stabilize it by up to 36%, even though the pure premium rate of WII will increase by 10% at 2050 and by 30% at 2100. For the first time, our study proves WII is one effective adaptation strategy for the most susceptible farmers under global warming and has the potential to be applied for other crops and countries.