Abstract: Abstract: Although fan-pad evaporative cooling system is a kind of energy-saving and environment-friendly cooling method, its application in beef cattle barn is still very rare. A negative pressure ventilation system for wet curtain fan was tested in this study to improve the summer environmental conditions of beef cattle barn in Southern China and find out its suitability for hot and humid climates. The study was conducted in 2 cattle beef barns located at Gao'an, Jiangxi Province, where is hot and humid in summer. The system consists of a cellulosic cooling pad and 4 axial flow fans with an air volume of 38 048 m3/h and an electric power of 1.1 kW. According to the results of the preliminary experiment, the operation time of the cooling system was from 09:00 to 19:00. In this study, simmental beef cattle were randomly allotted in 2 confined barns where feed and water were freely available. The data of environmental factors and beef physiology were collected. Temperature-humidity-velocity index (THVI) and heat load index (HLI) value were calculated to estimate the effects of climatic variable and heat accumulation. The cooling effect of the system was affected by the ambient temperature and relative humidity. With the ambient temperature increased by 1 ℃, the cooling effect increased by 0.6 ℃; with the relative humidity increased by 10%, the cooling effect decreased by 1.6 ℃ There was a temperature gradient along the airflow direction, and the temperature increased 0.033 ℃ for every 1 meter increase in the distance from the cooling pad. The air velocity parallel to the direction of the air?ow was also inconsistent. The air velocity near the cooling pad was higher than that at the fan outlet and the middle area (P<0.01), and the air velocity of the outlet of the fan was higher than that at the middle area (P<0.01). During the measurement period, the average temperature in the experiment barn was (29.7±0.5) ℃, compared with the control barn, decreased by 3.2 ℃ (P<0.01); the average relative humidity was (89.9±1.9)%, increased by 21.3% (P<0.01); the average air velocity near the cow was (0.75±0.02) m/s, increased by 0.30 m/s (P<0.01); the average effective temperature was (29.1± 0.4) ℃, decreased by 1.8 ℃(P<0.01); the average concentration of CO2 was (498±14) (10(6, deceased by 44 (10(6 (P<0.01) ; and the average concentration of NH3 was (3.63±0.33) (10(6. However, because of the high relative humidity, HLI value of the experiment barn was slightly higher than that of the control barn(P＞0.05). The average respiration rate in the experiment barn was (57±1)breaths/min, compared with the control barn, decreased by 13 breaths/min (P<0.01); the average skin temperature was (35.54±0.09) ℃, decreased by 0.92 ℃ (P<0.01); the average rectal temperature was (38.74±0.04) ℃, decreased by 0.11 ℃ (P＞0.05); and the average daily weight gain was (0.65±0.52) kg/d, increased by 0.13 kg/d (P＞0.05). The results indicated that fan-pad evaporative cooling system was able to improve the environmental conditions for beef cattle barns in Southern China, thus relieving heat stress of beef cattle. This provides a scienti?c basis for the extension and application of evaporative pad cooling systems in Southern China.