Abstract Extreme heat events have occurred more frequently in China in recent years,leading to serious impacts on human life and the health care system. To identify the characteristics of individuals with heat-related illnesses in China during the summer of 2013,we collected the data from the Heat-related Illness Surveillance System in Chinese Center for Disease Control and Prevention (China CDC). A total of 5758 cases were reported in the summer of 2013,mostly concentrated in urban areas around the middle and lower reaches of the Yangtze River. We found a difference in age distribution of percentage of deaths from heat-related illness between males and females. Severe cases in males mostly occurred in the age group 45-74 years but in females mostly in the age group over 75. A distributed lag non-linear model had been used to iden-tify population vulnerabilities in Ningbo and Chongqing. The results show that there was a clear positive relationship be-tween maximum temperature and heat-related illness,and the heat effect was nonlinear and could last for 3 days. The elderly and males in the range of45-64 years old might be the most vulnerable people of heat-related illness in China. We also highlighted some deficiencies of the surveillance system,such that the reported data were not accurate,comprehensive,or timely enough at this stage.