To explain the preservation mechanism of bamboo leaf antioxidant soaking combined with whey protein isolate coating on Se-rich rainbow trout (Oncorhynchus mykiss) at the protein level with physicochemical properties of protein. The Se-rich O. mykiss was cut longitudinally to fillets after beheading, gutting, and skinning. The Se-rich rainbow trout fillets (SRTFs) were immersed in 1.0% antioxidant of bamboo leaves (AOB) solutions (distilled water served as the control) followed by coating with whey protein isolate (WPI), then stored at 4 ℃ for 1, 4, 7, 10 and 13 d after the surface moisture on SRTFs was drained at 25 ℃. The myofibrillar protein and TCA-soluble peptides contents, and molecular bond, as well as total sulfhydryl content, surface hydrophobicity, and secondary structure of myofibrillar protein were measured, to investigate the effect of coating on the physicochemical properties of protein from Se-rich O. mykiss during cold storage. The results showed that the myofibrillar protein and β-sheet contents for the WPI group were significantly higher than the control during cold storage. From 1 to 7 days, the TCA-soluble peptides and disulfide bond contents, and surface hydrophobicity index (H₀) for the WPI group were significantly lower than the control, while total sulfhydryl content showed an opposite trend. However, these differences between the WPI group and control gradually weakened as the cold storage time prolonged, and there was no significant difference at 13 d. The myofibrillar protein, total sulfhydryl, hydrogen bond, α-helix, and β-sheet contents for the 1.0% AOB+WPI group were higher than the WPI group and control, while an opposite trend was observed for H₀ and the contents of TCA-soluble peptides, disulfide bond, and β-turn. The WPI film was formed on the surface of SRTFs, which can isolate the fillets from the air and alleviate microbial contamination. AOB contains flavonoids, polyphenols, etc., which can scavenge free radicals and inhibit the oxidation of sulfhydryl groups and the formation of disulfide bonds, leading to the delay of myofibrillar protein denaturation. In addition, the hydrophilic groups in polyphenols can reduce the surface hydrophobicity of myofibrillar protein and improve the solubility. These results indicated that AOB soaking combined with WPI coating inhibited the denaturation and degradation of myofibrillar protein, resulting in the delay of the quality attributes deterioration of SRTFs during cold storage.