Abstract: Abstract: There are high moisture and temperature in summer in the Southern China, and moisture and hot stress impact the feed intake of livestock, further impact the production properties of cattle. Many measurements such as overshadowing on top of the barn, fanning, and spraying cooling, additive in diet etc, were used to relief the hot stress of livestock. To improving the production properties of cattle, fanning in open-topped cowshed combining with chromium added to diet were investigation. A 2×2 factorial trial was conducted to determine the effects of fanning and chromium added to diet on thermal environment, physiological indexes and growth performance of beef cattle in summer in the Southern China. Thirty-six Simmental crossbred beef cattle ( average body weight 392.8 kg ) were chosen and randomly divided into 4 groups, and were raised in open feedlot barn for 30 days. In treatment 1 (T1), fans were installed and chromium nicotinate was added to beef cattle diet; In treatment 2 (T2), fans were only assembled; In treatment 3 (T3), chromium nicotinate was added to diet; In the control treatment (T4), the beef cattle were raised in feedlot barn without fans and without chromium nicotinate in diet. The dosage of chromium was 800 μg/kg. The indexes such as environmental factors, temperature-humidity index, rectal temperature, respiration rate, average daily gain and economic benefits were collected. The results showed as following: 1) Compared with the control barn without fan, average room temperature was lower by 1.9℃ (P < 0.01), wind speed was increased by 5.6 times (P < 0.01), THI reduce by 5.65% (P < 0.01) in 14:00 in treatment barn with fan. 2) For the cattle suffered from the heat stress, the respiration rate was reduced by 2.37 times (P< 0.01), and rectal temperature were reduced by 0.18℃ (P<0.01) by chromium supplementation, and the respiration rate was reduced by 6.97 times (P < 0.01) by fanning. No interaction effects on respiration rate and rectal temperature was obtained between chromium supplementation and fanning. 2) The average daily gain of beef cattle in T1 were increased by 44.16% (P < 0.05), 35.37% (P < 0.05) and 79.03% (P < 0.05) than that in T2, T3, and T4, respectively. Gross profit in rearing beef cattle in T1 was increased by 8.72 yuan per head per day than that in T4. In conclusion, both cooling by fans in feedlot barn and chromium supplementation relieved the heat stress of beef cattle, and the average daily weight gain was improved, and finally the economic benefits was increased. However, the combination use of the two measures leads to better results.