Global warming poses a serious threat to rice production and food security through increasing high-temperature stress. Identification of heat-tolerant genes and development of new heat-resistant varieties are crucial to mitigate the harm of high temperature. A set of RIL population， derived from the cross between the heat-sensitive variety Junambyeo （JNB） and the heat-tolerant variety Ganzaoxian58 （GZX58）， were developed to identify heat tolerance traits at the heading stage under natural extreme high-temperature stress conditions in 2022 year using a high-density genetic map. Natural high-temperature stress significantly reduced seed setting rate， with the RIL population showing continuous， approximately normal distribution， exhibiting highly significant correlations with control seed-setting rates and heat tolerance coefficients. Genetic mapping revealed six QTLs for spikelet number per panicle， filled grain number per panicle and spikelet fertility under control environment， and five heat tolerance QTLs （qHTSFI4， qHTSFII4， qHTC2， qHTC4 and qHTC6） under natural high temperature environment. These QTLs （qHTSFI4， qHTSFII4 and qHTC4） formed a major cluster qHTH4 on chromosome 4. High-density map analysis of extreme lines confirmed that qHTC2， qHTH4 and qHTC6 function in regulating heat tolerance with additive effects. The RIL lines stacking more than two major QTL had significantly enhanced heat resistance. Bioinformatics analysis identified 14 candidate genes within the target region， providing the foundation for the genetic improvement of heat tolerance and molecular characterization of underlying mechanisms in rice.