Intercropping is a popular cropping system in high-yielding production of food and feed in the world, which is more productive than monocropping because of the intensive utilization of natural resources, such as sunlight, heat, water and fertilizer. As a component crop in most intercropping systems, maize can be intercropped with a variety of crops, such as common bean, faba bean, soybean and peanut, showing an important role, and an obvious intercropping yield advantage. Maize‖peanut intercropping as an important cultivation pattern expanded rapidly in Sichuan Province and Huang Huai Hai Plain, China. We found maize‖peanut intercropping enhanced the efficient utilization of strong sunlight by maize and weak sunlight by peanut, thus leading to intercropping advantages. To elucidate the photosynthetic mechanism of intercropping yield advantage of maize, that is, whether the better utilization of strong sunlight results from higher absorption and transmission of sunlight or enhanced photosynthetic CO₂ assimilation, a field experiment was conducted to investigate the effects of maize‖peanut intercropping on the characters of response curves of Pn to PFD and to CO₂, fluorescence, and chlorophyll content and component of intercropped maize function leaves, dry matter accumulation and filling rate in 2010-2011 year at Henan University of Science and Technology Farm. Results showed that intercropping increased chlorophyll content of maize function leaves, altered chlorophyll component, significantly enhanced the net photosynthetic rate of maize function leaves, and delayed senescence in maize‖peanut intercroping system. Intercropping significantly enhanced light compensation point, light saturation point, the maximum net photosynthetic rate of light saturation point, apparent quantum yield and carboxylation efficiency, but didn't obviously affect the Fv/Fm,Φ_PSⅡ and qP of intercropped maize function leaves. Increased dry matter accumulation per plant of intercropped maize in the late growth stage was mainly attributed to the better growth of kernels, and significantly enhanced yield compared with sole-cropped maize. The partial land equivalent ratio (PLER) of maize was greater than the maize area ratio of maize‖peanut intercropping system by 106.6%-120.3%, displaying a significant intercropping yield advantage. It suggested that the intercropping yield advantage of maize mainly from the rise of net photosynthetic rate of function leaves in the late growth stage, and more allocation photosynthetic products to grains, which was due to the increase of carboxylation efficiency and apparent quantum yield, and strengthening of the ability to fix CO₂, but not the increase of sunlight energy transmission and conversion efficiency.