Abstract: Future climate change will bring considerable challenges to agricultural production and food security. Presently, research on the effects of elevated CO₂ concentration and increased temperature on crops is mostly focused on C₃ crops, while research on C₄ crops is rare. Maize is the most widely planted C₄ crop in the world, it is of great significance to explore the response of maize to elevated CO₂ concentration, increased temperature, and their combination to assess the impacts of future climate change on C₄ crops. The maize variety ‘Xianyu-335’ was used. Four treatments were set up in controlled chambers: CK (CO₂ concentration 400 μmol·mol⁻¹, ambient temperature), EC (CO₂ concentration 600 μmol·mol⁻¹, ambient temperature), ET (CO₂ concentration 400 μmol·mol⁻¹, 2 ℃ higher than ambient temperature), and ECT (CO₂ concentration 600 μmol·mol⁻¹, 2 ℃ higher than ambient temperature). The related indices of photosynthetic physiology, glucose metabolism, and nitrogen metabolism of maize leaves were measured at the grain-filling stage, and the biomass of maize was measured after ripening. The results showed that: 1) under elevated CO₂ concentrations, the chlorophyll content, sucrose content, net photosynthetic rate, sucrose synthase activity, pyruvate kinase activity, and α-ketoglutarate dehydrogenase activity in leaves were significantly increased (P<0.05), while glutamate synthase activity was significantly decreased (P<0.05). Additionally, aboveground biomass and spike mass were significantly increased by 35.8% and 170.2%, respectively (P<0.05). 2) At increased temperatures, the net photosynthetic rate, and activities of sucrose synthase and pyruvate kinase of leaves were significantly increased (P<0.05), while α-ketoglutarate dehydrogenase and glutamate synthase activities were significantly decreased (P<0.05), and the above-ground biomass and the biomasses of leaf, stem, and spike were significantly decreased by 37.0%, 28.7%, 32.3%, and 62.2%, respectively (P<0.05). 3) Under the combination of elevated CO₂ concentration and increased temperature, the net photosynthetic rate and pyruvate kinase activity of leaves were significantly increased (P<0.05), whereas the chlorophyll content, and activities of α-ketoglutarate dehydrogenase and glutamate synthase were significantly decreased (P<0.05), and the leaf biomass was significantly decreased by 23.4% (P<0.05). In conclusion, elevated CO₂ concentration could alleviate the negative impact of increased temperatures on maize biomass by increasing photosynthesis and the activity of enzymes related to glucose metabolism and photosynthetic metabolites. Under elevated CO₂, increased temperature, or their combination, nitrogen metabolism in maize is inhibited; thus, leaves are subjected to nitrogen stress, which harms maize quality.