[Objective] In order to explore the effect of adding yeast culture to the diet on the production performance and antioxidant capacity of dairy cows under high temperature in summer. [Method] Sixty healthy Holstein cows with similar physical condition were randomly divided into four groups, with 3 replicates in each group and 5 cows in each replicate. The control group was fed with basic diet, and groups I, II and III were fed with 10, 15 and 20 per day per head yeast culture respectively. The pre-test period is 7 days, and the formal test period is 21 days. [Result] Compared with the control group, the average daily feed intake of dairy cows in experimental group II and experimental group III increased significantly (P<0.05). The milk yield and 4% standard milk yield of dairy cows in groups I, II and III increased significantly (P<0.05), and the number of somatic cells in milk decreased significantly (P<0.05). The content of glucose in plasma of dairy cows in groups I, II and III increased significantly (P<0.05), while the content of β-hydroxybutyric acid decreased significantly (P<0.05). The total antioxidant capacity, the contents of catalase, superoxide dismutase and glutathione peroxidase of dairy cows in groups I, II and III were significantly increased (P<0.05). [Conclusion] Adding yeast culture to the diet at high temperature in summer can effectively improve the performance of dairy cows and enhance their antioxidant capacity, and the optimal dosage of yeast culture is 20 g/ head per day under this experimental condition.