Natural bioactive peptides often have poor functional properties and thermal stability， in order to improve the antioxidant ability and thermal stability of chicken lung peptides， plastein reaction involving pepsin and exogenous amino acids was used to treat peptides from chicken lung. High performance liquid chromatography (HPLC) was applied to compare the molecular weight changes before and after the reaction， while the properties of the substances were characterized by UV spectra， fluorescence spectrum， X-ray diffraction spectrum， scanning electron micrographs (SEM). Meanwhile， Fourier transform infrared spectrum (FTIR) and circular dichroism (CD) spectrum were employed to explore the changes of the secondary structure of peptide and plastein. The results showed: Firstly， the DPPHo free radical scavenging rate， chelating ability of Fe2+ and ·OH scavenging rate increased by 51.85%， 31.11% and 31.30% while the thermal denaturation temperature raised from 122.06 ℃ to 136.15 ℃ after 3% Cysteine supplementation. Secondly， the molecular weight and surface hydrophobicity increased， UV and fluorescence spectra showed that the changes of amino acid microenvironment improved the antioxidant activity. Thirdly， the X-ray diffraction pattern revealed that the main diffraction peak widened but the intensity decreased after the reaction， the SEM results displayed that the process involved hydrolysis and repolymerization of molecules. Finally， the results of FTIR and CD showed that the peptide molecules were stretched and the hydrophobic groups were exposed， which might be the reason for the improved antioxidant capacity of the peptides. In summary， plastein reactions changed the secondary and tertiary structures of proteins， thus effectively improving the antioxidant capacity and thermal stability of bioactive peptides.