In order to explore the effect of direct current (DC) and alternating current (AC) magnetic field (MF) on the biological (fruits and vegetables) phase transformation and ice crystal formation, we used carrot strips (0.5 × 0.5 × 1 cm3) and put them at low temperature control panel. The samples were frozen under AC and DC MF of 50 Hz with different intensities, i.e., 0, 0.46, 0.9, 1.8, 3.6, and 7.2 mT. The ice crystals formation during the process of cell freezing was observed and recorded using the optical microscope, and the beginning and ending time of the phase transformation with the corresponding temperatures were determined. The results show that the DC and AC MF situations compared to non-MF can decrease ice crystal volume and be more flocculent. The changes will reduce the cell membrane damage rate. The increase of magnetic field intensity delays the phase change time and leads to a shorter phase transition duration, a reduction in the cells’s lowest noncrystallization temperature is also observed. Such changes in thermal dynamic process and size elementary freezing (rapid formation of small ice crystals) reduce the damage to the quality of fruits and vegetables.