Climate change has significantly increased adverse effects on human health, and economic growth^1–3. However, few studies have differentiated the impacts of extreme temperatures at the city level, and analysed the future implications for human health under various climate change scenarios.^4–6 Here, data on historical relationship among six kinds of climate-sensitive diseases (CSD) hospitalizations and temperatures across 301 cities (over 90% of all cities) and more than 7,000 hospitals in China are leveraged, and a nonlinear distributed lag model is used. This study projects hospitalization risks associated with extreme temperatures through to the year 2100 and develops the Hospitalization Burden Economic Index to assess the burden under three carbon emission scenarios in cities. Five dimensions including spatial distribution, disease categories, population age groups, future time horizons, and carbon emission development pathways have been evaluated. Historical data specifically indicate more temperature-related risks among the CSDs in northwestern and southwestern China. Notably, gestation-related disease risk is associated with increased vulnerability to extreme heat in specific regions. The projections reveal that, under current thermal conditions with no adaptations, the excess hospitalizations from extreme heat will reach 5.1 million people by 2100 under the high emission scenario.These findings highlight the need for targeted climate change mitigation strategies to reduce uneven climate-related hospitalization risks and economic burdens while accounting for differences in city geography, extreme temperatures, population groups and carbon emission development pathways.