Abstract: The decrease in photosynthetic capacity caused by iron deficiency chlorosis is a key limiting factor affecting the improvement of peanut yield and quality in saline-alkali soil. To explore the effects of quinoa-peanut intercropping on iron nutrition, photosynthetic characteristics, and belowground response mechanisms of peanuts in saline-alkali soil, a field experiment combined with root separation methods was conducted. Four treatments were set up in the experiment including: peanut monocropping (MP), quinoa-peanut intercropping without separation (IPW), quinoa-peanut intercropping with nylon net separation (IPN), and quinoa-peanut intercropping with plastic sheet separation (IPP). The effects of different intercropping treatments on iron uptake and utilization, photosynthetic characteristics, soil physical and chemical properties, root morphology, and yield of peanut were analyzed. The results showed that compared with MP treatment, IPW treatment significantly increased the iron content and uptake in peanut plant organs at the seedling and pod-setting stages, enhanced the contents of chlorophyll and carotenoids, reduced the leaf yellowing rate, improved the net photosynthetic rate, and increased dry matter accumulation in the late growth stage, ensuring the pod yield of peanut. In contrast, IPN treatment improved the iron uptake and photosynthetic characteristics of peanuts to a certain extent at the pod-setting stage, but the effect was weaker than that of IPW. However, IPP treatment did not show any improvement in peanut iron uptake or photosynthetic characteristics. Additionally, IPW treatment reduced soil electrical conductivity by 28.85% and 14.27%, increased soil available iron content by 7.09% and 9.62%, and soil organic matter content by 17.28% and 29.52%, respectively. Root growth and morphological development of peanut at the pod-setting stage in IPW were better than those in MP. Correlation analysis showed that peanut iron uptake and peanut yield were negatively correlated with soil electrical conductivity, and significantly positively correlated with soil available iron content and root morphological development indicators such as total root length and root surface area of peanut. To summarize, IPW treatment can improve the iron nutrition of peanuts in saline-alkali soils, enhance peanut photosynthetic performance and dry matter accumulation. The reduction of soil electrical conductivity, increase of available iron content and optimization of root morphological structure are the underground response strategies of intercropping quinoa to improve iron nutrition of peanuts in saline-alkali soils.