Abstract: Heat stress for adult sows in summer is a technical problem, which always constrains pig production. A new water-cooled cover was exploited by using the underground water as the natural coolant based on the principle of radiant cooling. The objectives of this experiment were to study the cooling effect of the cover and the sows’ selective behavior of the lying area under different internal temperatures of the piggery. The results showed that when the ambient temperature of piggery and inlet water temperature of water-cooled cover were 31.3℃and 21.5℃, respectively, the black globe temperature inside the cover was 2.7℃lower than that outside the cover. Compared with the skin temperature and respiratory rate of the control group, that of the experiment group was significantly lower. When the ambient temperatures were between 23-27℃, 77% of sows lay on the outside exercising yard of the piggery, when the ambient temperatures were between＞27-31℃, 50% of sows lay under the cover, and when the ambient temperatures above 31℃, 75% of sows lay under the cover. The number of sows lying under the cover increased with the increasing of the environmental temperatures. This experiment shows that the water-cooled cover can effectively alleviate heat stress for sows when ambient temperature is above the thermal comfort zone of the animals.