Using up-to-date data of single-season rice phenology observation from 75 agro-meteorological stations and relevant daily temperatures from 1961 to 2015 across Yangtze River reaches,vital factor was identified through stepwise regression analysis of date series of heat induced loss and corresponding three factors.Based on relationship between yield loss and vital factor,critical value was calculated,and accordingly spatiotemporal characteristics of heat stress hazard were detected.Optimal function was implemented to fit the distribution of vital factor at each station,through comparisons among 10 distribution functions co-tested by Kolmogorov-Smirnov,Anderson-Darling and Chi-Squared methods.Intensity of heat stress hazard and its probability was integrated to represent risk of heat stress hazard.The results elucidated that the heat stress hazard was correlated to daily maximum temperature,but had little relationship with accumulated number of days and thermal time.The critical value of the maximum temperature was 38.9 ℃,39.5 ℃,40.2 ℃,and 41.5 ℃,corresponding to low,medium,high and heavy heat stress hazard respectively.The extent and frequency of heat stress hazard decreased from 1960 s to 1980 s,and increased since 1990 s.The number of low,medium,high heat stress hazard process was greater than that of heavy heat stress hazard process.At the decadal scale,the number decreased during 1960 s-1970 s-1980 s and increased from 1990 s.The minimum values of the number were identified at low,medium,high heat stress hazard level,while an obvious increasing trend after 2000 was existed at heavy heat stress hazard level.Integrated risk index showed that high risk was mainly located in Chongqing and eastern Sichuan Basin where should receive more attention.Generally,the heat stress hazard will tend to be more frequent and series,which can prompt us that the specific adaptive strategies are necessary for Yangtze River reaches to maintain rice production and cope with climate change.