Wet pad was installed at one end of the greenhouse, the suction ventilator installed in the other end. When the air in greenhouse is needed to cool down, the control system of fan will start, the indoor air is forced out and build-up the negative pressure; At the same time, the water pump water the wet pad. The negative pressure cause the indraft through the wet pad , leading to evaporation and cooling, then the cold air flow through the greenhouse, absorb the indoor heat, so as to achieve the purpose of the circulating cooling.