The mechanism by which the ternary complex of polyphenols, polysaccharides, and proteins acts on myofibrillar protein was herein explored and its potential to promote freezing resistance to aquatic products was evaluated. Sinapic acid (SA), chitosan (CS), and collagen (COL) were used as raw materials. The preparation conditions for sinapic acid-grafted chitosan (SA-g-CS) were screened through single-factor experiments and the grafted product was combined with COL to form a complex (SA-g-CSCOL). The effects of SA-g-CS-COL on the turbidity, endogenous fluorescence spectra, and secondary structure of tilapia myofibrillar proteins at room temperature were investigated, along with UV-Vis spectra and SDS-PAGE under freezing conditions. The optimal preparation conditions for SA-g-CS were pH 6.5, CS molecular weight 1 ku, reaction time 18 h, and SA:CS ratio 1:1, which yielded a grafting degree of 428.14 mg SAE•g-1. At room temperature, 0.4% SA-g-CS-COL complex reduced the endogenous fluorescence intensity and α-helical structure of myofibrillar protein by 3.49% and 27.45%, respectively, whereas turbidity, β-sheet and random coil increased by 39.09%, 30.43%, and 53.85%, respectively. During the freezing process, the UV absorption peak intensity of myofibrillar protein was enhanced and the protein band became thicker. Therefore, the SA-g-CS-COL complex prepared in this study can effectively delay the oxidative denaturation of tilapia myofibrillar protein during the freezing process, thus providing a theoretical basis for the application of polyphenol, polysaccharide, and protein ternary complexes for freezing resistance of aquatic products.