<p>Heatwaves are escalating under anthropogenic climate change, posing severe threats to socioeconomic development and public health. While global assessments point to rising risks, the cumulative thermal burden experienced by specific birth cohorts remains insufficiently quantified in China. This paper presents a high-resolution assessment to rigorously examine the lifetime exposure and vulnerability to heatwaves of Chinese populations born between 1990 and 2020. Specifically, the daily maximum temperature data from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2b) are employed to calculate the Heat Wave Magnitude Index daily (HWMId); lifetime cumulative exposure to heatwaves is quantified by integrating downscaled census data under certain Representative Concentration Pathways (RCPs); and the emergence of unprecedented exposure is assessed across diverse vulnerability strata. The results indicate that under the high-emission RCP8.5 scenario, the probability of heatwaves in China is expected to surge from 4.95% to 78.84% by the end of the century. There exists a substantial intergenerational disparity, with the 2020 birth cohort expected to face the exposure to heatwaves four times that of the 1990 cohort. This temporal disparity is further compounded by the imbalances across geographic and economic dimensions. Although the Gini coefficient of heatwave coverage drops from 0.38 under RCP2.6 to 0.10 under RCP8.5, the intensity of exposure remains negatively correlated with economic development. Under RCP8.5, populations in low-income provinces (e.g., Xizang, Qinghai, and Gansu) face exposure levels 1.5 times the national average, whereas only 6% of the population in high-GDP regions exceeds the average burden. Overall, this paper underscores that socioeconomically vulnerable groups would bear the brunt of intensifying heat risks and highlights the urgency for targeted adaptation strategies.</p>