Abstract: In order to obtain good preservation quality in the processing of aquatic pre-made products with silver carp (Hypophthalmichthys molitrix) as raw material, we designed a new freezing method. We investigated the structural and functional changes of myofibrillar protein (MP) by freezing alginate oligosaccharides (AO) at a mass fraction of 0.6% with a low magnetic field (LMF) of 2 mT, and used no treatment at −20 ℃ as the blank group. On this basis, we added AO and AO+LMF as the experimental group, added AO as the common freezing (CF) group at −30 ℃, and had frozen the MP for 28 d. By measuring the solubility, turbidity, surface hydrophobicity, sulfhydryl content, thermal stability, Fourier transform infrared spectroscopy and endogenous fluorescence spectroscopy, we comprehensively compared the structure and properties of frozen MP. The results show that there were no significant differences in the turbidity among the three freezing methods at −20 ℃. The protein solubility of CF group was 94.11%. After AO+LMF treatment, the exposure of hydrophobic groups reduced, with a higher total sulfhydryl content of 15 mmol·kg⁻¹, and the exposure of tryptophan residues reduced, which protected its protein tertiary structure effectively. Fourier transform infrared spectroscopy shows that after AO modification and freezing, MP denaturation was the lowest, α-helix content was higher, and secondary structure was more stable. It it showed that 0.6% fucoidan with low magnetic field freezing treatment can better maintain the stability of MP in silver carp, which lays the foundation for the application of AO in frozen aquatic products and provides references for the further research on the low magnetic field freezing.