The invention discloses an antioxidant peptide, its preparation method and application, and aims to provide an antioxidant peptide with high-efficiency antioxidant activity derived from chicken breast myofibrillar protein, its preparation method and application. The amino acid sequence of the antioxidant peptide of the present invention is ITTNPYDY or IGWSPLGSL. The preparation method of the antioxidant peptide comprises the following steps: extracting myofibrillar protein from fresh chicken breast meat, enzymatically hydrolyzing the obtained myofibrillar protein with pepsin, and obtaining the antioxidant peptide through separation, purification and synthesis techniques. The antioxidant peptide of the present invention is a new type of antioxidant peptide, which has strong antioxidant activity after testing, and its iron ion reduction ability and oxygen free radical absorption ability are significantly higher than those of glutathione under the measurement conditions of the present invention , and at the same time, it has a significant inhibitory effect on the oxidative damage of NIH‑3T3 cells. The antioxidant peptide of the invention belongs to natural antioxidants, is safer to eat, and can be applied to antioxidant functional foods, health care products and medicines.