Abstract: The Huang-Huai-Hai summer maize region is a dominant maize producing area in China. Adverse climates, such as high-temperatures and heat damage, occur frequently during maize growing season and have a great impact on maize production. The effects of high-temperature stress on leaf photosynthetic performance and yield traits of maize hybrids as well as their parent inbred lines were studied to provide a theoretical basis for the breeding and popularization of high-temperature-tolerant maize varieties. ‘Jingnongke728’ ‘MC812’ ‘Xianyu335’ ‘Zhengdan958’ and their parental inbred lines were used, high-temperature treatments from the bell-mouthing stage to 7 d after silking were conducted, and the effects of high-temperature stress on the relative content of chlorophyll, photosynthetic characteristics, F_v/F_m, photosynthetic enzyme activity, yield and yield components were studied. Compared to field control, the relative chlorophyll content, net photosynthetic rate, stomatal conductance, and F_v/F_m of different hybrids and their parent inbred lines decreased under high-temperature stress pre- and post-flowering. The decreases of hybrid ‘Jingnongke728’ and parent inbred line ‘Jing2416’ were the smallest. The intercellular CO₂ concentration and transpiration rate displayed an increasing trend, with ‘Jingnongke728’ and ‘Jing2416’ having the smallest increase. The activities of phosphoenolpyruvate carboxylase, ribulose 1, 5-diphosphate carboxylase, catalase, and superoxide dismutase in the ear leaves of maize hybrids and their parent inbred lines decreased under high-temperature stress pre- and post-flowering. High-temperature stress pre- and post-flowering reduced ear row number, kernel per row in maize hybrids and their parent inbred lines, decreasing yield. The yields of hybrids ‘Jingnongke728’ ‘MC812’ ‘Xianyu335’ and ‘Zhengdan958’ decreased by 3.18%, 5.00%, 50.61%, and 9.50%, respectively. Among the parent inbred lines, ‘Jing2416’ had the smallest decrease in ear row number, kernel per row and yield, whereas the yield of ‘PH6WC’ had the largest decrease. ‘Jingnongke728’ ‘MC812’ and their male parent ‘Jing2416’ had higher relative chlorophyll content, photosynthetic capacity, and protective enzyme activity under high-temperature stress pre- and post-flowering, and their yield was less affected by high-temperature; thus, they have better heat tolerance.