Abstract: In preset study, the prevention and treatment experiments were conducted to evaluate the effect of ＂Beiermei＂, a commercial product of premix with main components of minerals, on lactating performance of dairy cow. In prevention experiment, a total of 20 healthy lactating dairy cows were chosen and divided into control group （group A） and experimental group （group B）. In treatment experiment, a total of 20 lactating dairy cows with subclinical mastitis were selected and also divided into control group （group C） and experimental group （group D）. There were 10 dairy cows for group A, B, C and D. The two control groups, group A and group C, fed basal diet, and the two experimental groups, group B and group D, fed basal diet adding with＂Beiermei＂ with dosage of 300 mg/kg. The daily milk yield of each group were recorded, and the milk samples were collected at 0, 15, 30, 45 and 60 d of formal experiment and milk composition was determined, respectively. The prevention experiment results showed that compared with group A, the average daily milk yield for each cow of group B was increased by 1.90 kg （P〉0.05）, and the percentage of milk fat, milk protein, milk sugar and content of dry matter were increased by 3.52% （P〉0.05）, 7.21% （P〉0.05）, 1.92% （P〉0.05） and 6.09% （P〈0.05）, respectively. The treatment experiment results showed that compared with group C, the average daily milk yield for each cow of group D was increased by 2.24 kg （P〈0,05）, and the percentage of milk fat, milk protein, milk sugar and content of dry matter were increased by 14.42% （P〈0.05）, 10.65% （P〈0.05）, 2.02% （P〉0.05） and 9.53% （P〈0.05）, respectively. The commercial product of premix＂Beiermei＂with main components of minerals has prevention and treatment effect on subclinical mastitis of dairy cow and can also improve the quality of milk.