Intercropping is used widely by smallholder farmers in developing countries to increase land productivity and profitability.  We conducted a maize/peanut intercropping experiment in the 2015 and 2016 growing seasons in Shandong, China.  Treatments included sole maize (SM), sole peanut (SP), and an intercrop consisting of four rows of maize and six rows of peanut (IM and IP).  The results showed that the intercropping system had yield advantages based on the land equivalent ratio (LER) values of 1.15 and 1.16 in the two years, respectively.  Averaged over the two years, the yield of maize in the intercropping was increased by 61.05% compared to that in SM, while the pod yield of peanut was decreased by 31.80% compared to SP.  Maize was the superior competitor when intercropped with peanut, and its productivity dominated the yield of the intercropping system in our study.  The increased yield was due to a higher kernel number per ear (KNE).  Intercropping increased the light transmission ratio (LTR) of the ear layer in the maize canopy, the active photosynthetic duration (APD), and the harvest index (HI) compared to SM.  In addition, intercropping promoted the ratio of dry matter accumulation after silking and the distribution of ¹³C-photosynthates to grain compared to SM.  In conclusion, maize/peanut intercropping demonstrated the potential to improve the light condition of maize, achieving enhanced photosynthetic characteristics that improved female spike differentiation, reduced barrenness, and increased KNE.  Moreover, dry matter accumulation and 13C-photosynthates distribution to grain of intercropped maize were improved, and a higher grain yield was ultimately obtained.