Freezing is a common method of food preservation, but the traditional freezing method causes the formation of a large number of irregular ice crystals, which affects the taste and nutritional value of aquatic products. In this study, a static magnetic field-assisted freezing system based on an impact freezer was established to improve the freezing quality and reduce the adverse effects of freezing on aquatic products. The effects of static magnetic fields with different intensities （20 Gs, 40 Gs, 60 Gs, and 80 Gs） on the moisture distribution and physicochemical properties of frozen Penaeus japonicus were investigated. The results showed that the static magnetic field-assisted freezing technique shortened the phase transition time, and the higher the magnetic field intensity, the shorter the phase transition time. In terms of moisture distribution, the magnetic field-assisted freezing technique significantly reduced the thawing loss, cooking loss, and centrifugal loss. Among them, the cooking loss and centrifugal loss of the SMF-80 group were not significantly different from those of the fresh group, indicating that the magnetic field-assisted freezing can effectively reduce moisture loss of Penaeus japonicus. LF-NMR showed that the static magnetic field reduced the mobility and loss of fixed and free water. In addition, the static magnetic field accelerated the freezing rate and suppressed the increase of L* value in shrimp samples, and the DSC analysis showed that the thermal stability of of Penaeus japonicus proteins increased, indicating that the application of static magnetic field could reduce the damage to the protein structure.The static magnetic field also significantly improved the hardness, chewiness and resilience of Penaeus japonicus after freezing and thawing, and enhanced the texture of Penaeus japonicus. In conclusion, the static magnetic field-assisted freezing system effectively improved the quality of frozen Penaeus japonicus and minimized the adverse effects of freezing on the nutritional value of Penaeus japonicus.