The invention relates to a controlling method of the discharge of coolant medium, and more particularly to a controlling method of the discharge of coolant medium in the heat exchange wind box. By mainly controlling the discharge of coolant medium in the heat exchange wind box, it is able to directly control the volume of discharged coolant medium that supplies the circulation need of the heat exchange tube according to the variations of the target volumes of environmental heat energy in the freezing and air-conditioning area. Therefore, it increases the operation efficiency of the freezing and air-conditioning equipment and achieves the heat balance stability of the freezing and air-conditioning area. Furthermore, by saving the circulated volume of the coolant medium, it achieves the energy saving objective.