Abstract: The largeseed peanut cultivar of Huayu 22 was used to study the differences of canopy microenvironment, photosynthetic characteristics, and pod yield at three singleseed sowing densities, i.e., 225000 (S₁), 195000 (S₂) and 165000 (S₃) holes per hectare, in field experiments. The results showed that the canopy light transmittance, canopy air temperature and canopy CO₂ concentration all increased at these three single-seed sowing densities compared with those of double-seed sowing pattern (150000 holes per hectare), while the canopy humidity decreased. It seemed that singleseed sowing was helpful to improve microenvironment and the growth of peanut, especially at late growth stage. Meanwhile, the photosynthetic pigment contents and the net photosynthetic rate of peanut under singleseed sowing, especially in S₂ and S₃, were remarkably higher than those under traditional doubleseed sowing. S₂ had the optimum population size with an equal distribution of individuals, which reduced the contradiction between individuals and population, optimized the canopy microenvironment, enhanced the photosynthetic characteristics, and increased the synthesis and accumulation of photosynthetic products to maximize the yield production of peanut.