In order to explore the effect of DC and AC magnetic fields on the biological (fruits and vegetables) phase transformation and ice crystal formation, we used carrots strips (0.5×0.5×1cm3) and put them at low temperature control panel. The samples were frozen under AC and DC magnetic field of 50Hz with different intensity, i.e. 0,4.6,9,18,36 and 72Gs. The ice crystals formation during the process of cell freezing was observed and recorded using 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 magnetic field situation compared to non using magnetic field can decrease ice crystal volume and be more flocculent. Such change will reduce the cell membrane damage rate of. The increase of magnetic field intensity delay the phase change time and induces short phase transition duration, A reduction in the cells's lowest non-crystallization temperature was also observed. Such change in thermal dynamic process and size elementary freezing (rapid formation of small ice crystals) reduces the damage of fruit and vegetable and increase the product quality.