Abstract: To clarify the spatiotemporal distribution patterns of high temperatures before and after the flowering stage of summer maize in the North China Plain (NCP) under the background of climate change and their impacts on yield, this study collected daily meteorological data from 340 meteorological stations in the NCP (1981–2022), phenology data of summer maize from 19 agricultural meteorological stations, and high-temperature experimental data from published literature. High temperature thresholds of 32, 35, and 38 ℃ were selected to calculate high temperature indicators including extreme growing degree days (EDD) and the extreme heat days (EHD) and then their spatiotemporal distribution characteristics during the tasseling and grain-filling stages of summer maize were analysed in the NCP. Furthermore, the study conducted an equation to assess the impact of high temperatures before and after the flowering stage on yield reduction rate of summer maize and calculated the probability of high-temperature occurrence in different provinces during various growth stages. The study results showed that 1) under the background of climate warming, high temperatures in the North China Plain intensified. EDD and EHD more than 32, 35, 38 ℃ during the growing season of summer maize showed an increase trend (P < 0.05), with the increasing rates of 13.8 ℃·d/10a and 4.0 days/10a, 4.0 ℃·d/10a and 2.3 days/10a, and 0.4 ℃·d/10a and 0.4 days/10a, respectively. 2) The occurrence of high temperatures during the tasseling stage followed a pattern of more in the south and less in the north. During the grain-filling stage, high temperatures showed a spatial distribution characteristic of more in the southwest and less in the northeast. High temperatures during the tasseling and grain-filling stages showed an increasing trend during the past four decades. Based on the threshold temperature of 38 ℃, during the tasseling stage, significant warming occurred in northern Henan province, with the increase rates of 0.4 ℃·d and 0.5 days per 10 years, respectively. In southern Henan province and Renxian County in Hebei province, significant warming was also observed, with the increase rates of 0.4 ℃·d/10a and 0.5 day/10a for EDD and EHD, respectively. 3) The provinces with the highest probabilities of high temperatures above 32, 35, 38 ℃ before and after flowering were all found to be in Henan Province. The impact threshold of high temperature for the main maize varieties cultivated in the NCP is approximately 35 ℃. For each 1 ℃·d increase in accumulated harmful temperature more than 35 ℃, the yield reduction rate of summer maize increased by 0.45%. In the 2010s, the impact of high temperatures before and after flowering was particularly significant in Henan Province. Yield reduction rates in areas such as Jiaozuo in the southern part of the province and Huaibin in the southeastern part ranged between 2% and 5%. The findings of the study provide scientific support for accurately assessing the high-temperature risks and developing disaster reduction strategies at different growth stages of summer maize in the North China Plain in the context of climate change.