Dairy cows are suffering from serious heat stress in the shed with a single-color steel roof. In this study, a reflective film was pasted over the floor for better thermal insulation from the roof at ambient temperature. Two cowsheds were simulated with a similar building structure, one of which was reformed by pasting a reflective film over a single-color steel roof (film shed), and another of which was not reformed as a control (control shed). 90 growing dairy cows were raised in each shed. The measurement was performed on the inner surface temperature of the enclosure structure in the cowsheds and the indoor temperature. Moreover, the physiological parameters, antioxidant, immune properties, and production performance of cows were utilized to evaluate the effects of a single-color steel roof covered with the reflective film on the heat stress of cows in the hot season (from July to August) and non-hot season (from September to October). The results were as follows. 1) The inner surface temperature of the roof in the film shed decreased by 10.48 ℃ for the noon period from 12:00 to 13:00, compared with the control shed (P<0.01), whereas, the indoor ambient temperature decreased by 0.87 to 1.04 ℃ (P<0.05) for the phase from 09:30 to 13:30, during the hot season from July to August. The surface temperature of the roof in the film shed decreased by 8.16 ℃ for the noon phase, compared with the control shed (P<0.01) during the non-hot season from September to October. Besides, the duration of cows under moderate heat stress was 2.08% less in the film shed than that in the control shed every day during the period from July to August. By contrast, there was no heat stress in the two experimental sheds during September and October. 2) The respiratory rate of cows in the film shed was 58.33 times per minute, which was 12.51% lower than that in the control shed (P<0.01); the lying ratio of cows from 10:00 to 14:00 increased by 7.90% to 18.77% (P<0.05) during the period from July to August. After the growing dairy cows calved, the film shed demonstrated an increase of 7.20% in the milk yield (P=0.08) and 4.85% in milk protein rate (P<0.05) compared with control shed. 3) The concentrations of serum superoxide dismutase and total antioxidant capacity in the film shed increased by 5.71% and 10.47%, respectively (P<0.05), and the malondialdehyde concentration was reduced by 15.45% (P<0.05) from July to August, compared with the control shed. The serum concentrations of interleukin-4, interleukin-6, immunoglobulin G, and immunoglobulin M in the film shed were higher than those in the control shed (P<0.05) during the period from July to August. Particularly, the serum concentration and mRNA expression level of IL-4 increased by 24.78% and 25.43% respectively (P<0.01). In addition, the serum concentrations of interleukin-6, immunoglobulin G, and immunoglobulin M in the film shed increased by 9.06%, 18.58%, and 21.23%, respectively, compared with the control shed. The serum concentrations of HSP60 and HSP70 decreased by 14.06% and 15.87% during the hot season, respectively (P<0.05), compared with the control shed, and the expression level of HSP70 mRNA also decreased (P<0.05). However, there was no significant difference in the parameters between the two sheds during the period from September to October (P>0.05). In conclusion, the reformed single-steel roof had a significant heat-insulating effect during the period from July to August, and improved the blood physiological indicators, antioxidant and immune properties of growing dairy cows, which would effectively alleviate heat stress of cows, and improved its lactation performance after calving.