Abstract: 【Objective】 The study aimed to evaluate the effectiveness of Ru Ning Powder addition to TMR diet in prevention and treatment of dairy cow’s subclinical mastitis by measuring their milking performance,blood physicochemical indexes and antioxidant capacity.【Method】 Four hundred high-yielding cows were employed,and they was divided into four groups as follows:Ru Ning Powder addition group（140 g Ru Ning Powder were added to the feed for each cow per day,suffering from subclinical mastitis）,microecological preparation addition group（100g microecological preparation were added to the feed for each cow per day,suffering from subclinical mastitis）,control group（normal feeding,suffering from subclinical mastitis） and blank group（normal feeding,no subclinical mastitis）. The period of trial was 30 days.The number of somatic cell and milking performance of four groups of cows were determined on the day before dosing and on the 30th day after dosing. Eight cows in each group were selected for blood collection,milk collection,and for analyzing serum metabolism,antioxidant indicators（SOD,GSH-PX,T-AOC and more） and pro-inflammatory factor indicators（IL-1、IL-6、IL-8 and TNF-α）.【Result】 Ru Ning Powder addition groups had no significant differences in milking performance and serum metabolism with the control and blank groups（P＞0. 05）. The somatic cell counts of both Ru Ning Powder addition group and blank group was significantly different from the control group（P＜0. 05）. The antioxidant capacity of Ru Ning Powder group was significantly different from the control and blank groups（P＜0. 05）,while it did not significantly differ with microecological group. In Ru Ning Powder group,the contents of IL-1、IL-6、IL-8and TNF-α were significantly different with the control group（P＜0. 01）,and the decreasing amplitude was higher than that of the microecological group.【Conclusion】 The results showed that Ru Ning Powder addition to the feed could effectively prevent and cure subclinical mastitis of dairy cows,with no effects on milking and health of them.