Abstract: This study aims to determine the conflict between ventilation and thermal insulation in winter fattening sheepfolds in the northern China. 216 healthy male small-tailed Han sheep were selected as the experimental animals with the similar initial body weights (33.99 ± 1.25) kg. Three ventilated pens were randomly allocated at the Balin Left Banner experimental base in Inner Mongolia Autonomous Region, including the conventional ventilation, reverse ventilation 1 (the ventilation exchange system), and reverse ventilation 2 (the ventilation exchange system + air-source heat pump). The basal diet of the experimental sheep consisted of peanut straw, corn, soybean meal, corn distillers grains, wheat bran, and premix. The effects of these ventilation modes were systematically investigated on the production performance, serum parameters, slaughter characteristics, meat quality, and economic profit. The results demonstrated that no significant daytime difference was detected between indoor and outdoor temperatures under conventional ventilation. Whereas the indoor temperature was 5.6 ℃ higher at night (P < 0.05). The conventional ventilation was provided the effective insulation only during the nocturnal period, and there was a strong influence of the external temperature during the day. In contrast, the indoor temperatures were significantly higher than the outdoor ones under both reverse ventilation 1 and reverse ventilation 2. The mean values were consistently maintained above 6.2 ℃ under conventional ventilation in the entire diurnal cycle (P < 0.05). The reverse ventilation was effectively modulated the temperature differential between the shed's interior and exterior, thereby achieving the sustained thermal insulation within the facility. The sheep in the reverse ventilation 1 exhibited the significant increases in the final body weight (3.8%), average daily gain (5.4%), and feed intake (1.9%), compared with the conventional ventilation (P < 0.01). Both reverse ventilation systems were significantly enhanced the antioxidant capacity and immune function of the sheep (P < 0.05). Reverse ventilation 1 shared the superior slaughter performance and meat quality parameters, compared with the conventional ventilation and reverse ventilation 2 (P < 0.05). Both reverse ventilation 1 and reverse ventilation 2 significantly increased the level of color a* and the proportion of unsaturated fatty acids in the fattening mutton (P < 0.05). The economic profit of the reverse ventilation 1 was 0.14 yuan higher per head per day than that in the conventional ventilation, and 0.44 yuan higher per head per day than that in the reverse ventilation 2. The reverse ventilation was effectively resolved the ventilation-insulation paradox in the northern winters. Environmental conditions (reducing humidity and CO₂ concentrations) were improved to mitigate the oxidative stress. Ultimately, the growth performance was enhanced to optimize the long-chain fatty acid profiles in mutton. Notably, the reverse ventilation 1 was achieved in the better husbandry, compared with the heat pump-supplemented reverse ventilation 2. The reverse ventilation mode (the ventilation exchange) was greatly contributed to the ventilation and insulation in the sheep pens of the northern regions during winter. A better pen feeding and economic profit can also be gained for the fattening sheep in northern regions during winter.