The invention discloses a method for preparing peanut antioxidant peptide by fermentation, and the method comprises the following steps: adding distilled water to low-denatured degreased peanut protein powder, ultrasonically dispersing and dissolving, adjusting the pH value, sterilizing and cooling; inoculating with strain seed culture liquid, and fermenting and culturing; and carrying out ultrasonic-assisted enzymolysis, inactivating enzyme, centrifuging, and freeze-drying supernatant to obtain the peanut antioxidant peptide. The peanut antioxidant peptide prepared by the method disclosed by the invention has the antioxidant activities of scavenging hydroxyl free radical, superoxide anion free radical and DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical, inhibiting hydroxyl-free-radical-mediated deoxyribose injury, inhibiting peroxidation of lipidosome, resisting oxidation of linolic acid system, resisting grease peroxidation capability and the like, and has iron reduction capability, molybdenum reduction capability, iron ion chelating capability and copper ion chelating capability; and the method is simple to operate, has mild reaction conditions and is suitable for industrial production.