Microencapsulation technology based on sodium alginate hydrogels can be used to optimize freezing and rewarming procedures and to reduce cryo-damage to cells and tissues. This study first observed the morphology of oocytes of sodium alginate hydrogels at different volume fractions (0.5%, 1.0%, 1.5%, and 2.0%) to determine the safe concentration for their encapsulation. Second, the crystallization temperature and crystallization behavior of sodium alginate hydrogels with different volume fractions were systematically investigated using cryo-microscopy, and the morphology and crystallization of oocytes were compared when they were cooled down/retempered in the base solution (cryoprotectant solution). Finally, the freezing effects of the sodium alginate antifreeze hydrogel-encapsulated oocytes prepared by solvent replacement and physical mixing were compared. The results revealed that oocytes maintained their overall morphology and volume better in sodium alginate gels at volume fractions of 0.5% and 1.0%. Furthermore, oocytes in both the 1.0% sodium alginate group and the cryoprotectant solution group of 12.5% DMSO + 12.5% EG + 0.5 mol/L trehalose did not produce intracellular ice during the cooling process. Additionally, compared with the physical mixture, oocytes in the hydrogel solvent replacement group did not produce intracellular ice during the cooling process, and the cells retained their normal morphology after rewarming.