Abstract: Objective: To investigate the preservative effect of grape seed proanthocyanidin (GSP) on aquatic products. Methods: Salmon salar was utilized as the model subject. The regulatory effects of different GSP concentrations on quality characteristics, including physicochemical properties, freshness, texture properties, muscle microstructure, and protein oxidation, were investigated throughout refrigerated storage (4 ℃)at intervals (0 d, 3 d, 6 d, 9 d, 12 d). The mechanism by which GSP influences the structure of myofibrillar protein (MP) was analyzed using fluorescence spectroscopy and circular dichroism (CD) spectroscopy. Results: By the end of storage, compared with the control group, pH variations were reduced and water-holding capacity was significantly increased (P<0.05) in GSP-treated groups. The increase in total viable count (TVC) was significantly inhibited (P<0.05). The exceeding of the upper limit for total volatile basic nitrogen (TVB-N) was delayed by 3 days in the 0.75 mg/mL GSP treatment group. The carbonyl content of MP was reduced by 7.31%−18.27%, and the retention rate of total sulfhydryl groups was increased by 2.8%−12.1%. The structural integrity of myofiber bundles was significantly improved. Fluorescence spectral analysis revealed that GSP bound to MP via a static quenching mechanism, inhibiting the exposure of tryptophan residues. CD spectroscopy results demonstrated that the reduction rate in α-helices proportion (19%) was significantly lower in the 0.75 mg/mL GSP group than in the control group (34%), confirming its stabilizing effect on protein secondary structure. Conclusion: It is comprehensively demonstrated that the quality of salmon during storage is more effectively maintained by GSP through the modulation of protein oxidation pathways and molecular conformation. This study can provide a theoretical basis for natural antioxidant preservation technologies in aquatic products.