[Objective] To explore the effects of compound enzyme preparation on milk composition and milk yield of lactating cows. [Method] Sixty lactating cows were divided into 2 groups with 30 cows in each group, which were control group and compound enzyme preparation group respectively. The control group was fed only the basal diet, and the compound enzyme preparation group was fed 20 g of compound enzyme preparation every day on the basis of the basal diet. Milk yield and milk composition were measured after 12 weeks. [Result] Compared with the control group, the daily and weekly milk yield of lactating cows in the compound enzyme preparation group was significantly increased（P>0.05）. Compared with the control group, the contents of fat, protein, lactose and non-solid matter in milk of dairy cows in compound enzyme preparation group were significantly increased （P>0.05）. [Conclusion] Complex enzyme preparation can improve milk yield and milk composition in the middle stages of lactation.