Abstract Irrigation impact on heat comfort is controversial due to its opposing effects of cooling and humidification, especially over the North China Plain under global warming. While heat stress indices exhibit different responses, the omission of dynamic vegetation adds further uncertainty. Therefore, we apply WRF with improved crop systems to understand how irrigation affects humid heat stress under global warming. Wet‐bulb temperature (TW) and simplified wet‐bulb globe temperature (SW) used to measure heat stress show opposite responses in summer: TW increases due to its sensitivity to humidification on dry‐heat days, while SW decreases due to its sensitivity to cooling on wet‐heat days. Both heat stress changes are worsened under SSP5, and omitting dynamic vegetation results in noticeable underestimation of irrigation response, underscoring the need for model advancement. However, while irrigation substantially alters temperature and relative humidity, its combined effect on humid heat stress is insignificant compared to global warming.