The present invention provides a heat humidity independently controlled air conditioning system applied to IDC machine room and a refrigeration method. The air conditioning system comprises a closed type cooling tower, a water-cooling refrigeration unit, a cold water tank, a refrigerated water pump, a cold water pump, a dry coil module, a fresh air dehumidification module, an exhaust device, an embedded control system, a closed cooling tower inlet air wet-and-dry-bulb temperature sensor, a dry coil module inlet water temperature sensor, and a dry coil module outlet water temperature sensor. The refrigeration method is as follow: when the dry bulb temperature of the outdoor air is lower than the criterion temperature 1, the closed type cooling tower operates in the dry conditions, the water-cooling refrigeration unit stops, and thus water and energy are saved; when the dry bulb temperature of the outdoor air is higher than the criterion temperature 1 and the wet bulb temperature is lower than the criterion temperature 2, the closed type cooling tower operates in the wet condition, the water-cooling refrigeration unit stops, and thus energy is saved; and when the wet bulb temperature of the outdoor air is higher than the criterion temperature 2, the water-cooling refrigeration unit operates and during the operation process the outlet water temperature is the criterion temperature 2, and thus energy is saved.