The invention discloses a ferrous sulfate solution refrigerating crystallization device. The ferrous sulfate solution refrigerating crystallization device comprises a refrigerating machine, a refrigerating crystallizer and a heat exchange tube arranged in the refrigerating crystallizer as well as a refrigerating capacity adjusting tank, wherein a clapboard is arranged in the refrigerating capacity adjusting tank and used for dividing the refrigerating capacity adjusting tank into an A region and a B region which are communicated; a water inlet of the A region is communicated with a chilled water outlet of the refrigerating machine through a first valve; a water outlet of the A region is communicated with a chilled water inlet of the refrigerating machine; a water inlet of the B region is communicated with a water outlet of the heat exchange tube through a second valve and is also communicated with the chilled water outlet of the refrigerating machine through a third valve; and a water outlet of the B region is communicated with a water inlet of the heat exchange tube. The ferrous sulfate solution refrigerating crystallization device is characterized in that the water temperature of the B region is adjusted for ensuring that the temperature difference between incoming water and outgoing water of a heat exchange pipeline in the crystallizer in the refrigerating process is constant, i.e. the refrigerating capacity supplied to the refrigerating crystallizer is a steady state value, and therefore, the refrigerating capacity of the needed refrigerating machine is constant, the stable running of the refrigerating machine is ensured, and simultaneously ferrous sulfate in a solution can be prevented from locally supercooling and crystallizing to attach to the wall of the heat exchange tube.