Loach protein was hydrolyzed by neutrase to prepare antioxidant peptide in this study. Plastein reaction was used to modify loach protein hydrolysates for enhancing the scavenging ability of DPPH free radical of peptides by papain. The influences of the types of added amino acids, the extrinsic glycine dose,the substrate/ enzyme ratio, pH papain. The influences and hydrolsis time on scavenging ability of DPPH free radical of the Plastein reaction modification of loach protein hydrolysates were investigated by using single factor analysis method. On this basis,the optimal technology conditions for Plastein reaction modification of antioxidant peptide from loach protein was obtained by response surface methodology. Results showed that the optimal conditions for Plastein reaction modification of antioxidant peptide from loach protein were as followings substrate concentration at 40%, extrinsic close of histidine at 0.5