Abstract: Summer-sowing peanut has developed rapidly with a planting model of peanut-wheat relay cropping. However, studies on individual development and population structure of summer-sowed peanut were inadequate. To supplement this deficiency, a field experiment was conducted in 2014 and 2015, to study the differences in plant development, leaf physiological characteristics and yield components between single-seed (SS) and double-seed (DS) sowed summer peanut. The previous crop was wheat, which was harvested on June 15. The peanut cultivar ‘HY22’ was sowed on ridges and mulched with plastic film on June 20. The ridge was 50 cm with a furrow spacing of 30 cm. Plant spacing was 10 cm for SS, 20 cm for DS, and the plant density was same for both treatments, 2.5 × 10⁵ plant·hm². The results showed that main stem height and lateral branch length of SS treatment were higher than those of DS treatment at the early growth stage, however they became lower than those of DS at the late growth stage. The numbers of both node and leaf in main stem, leaf area index and especially branch numbers of SS were all higher than those of DS during the whole growth period. The activities of SOD, POD and CAT, chlorophyll content and photosynthetic rate increased, while MDA content reduced at pod-filling stage and maturation stage in SS treatment. Although no significant differences was observed on above leaf physiological indexes between SS and DS treatments at pod-filling stage, but the differences was remarkable at maturity stage. Pod yield of SS increased significantly compared with DS treatment due to a significant increase in full pod number per plant. And it positively related to both pod weight per plant and photosynthetic rate. This implied that it was positively correlated with economic coefficients, leaf number per main stem, leaf area index and chlorophyll content.