[Objective] To study the effects of adding bacterial enzyme preparations to dairy cow diet on blood biochemical and immune indexes.[Method] A total of 200 healthy lactating cows with similar age and parity in a large-scale dairy farm were selected as the research objects and divided into 4 groups（n=50） by random number table method.They were divided into control group（basic diet）,bacterial enzyme preparation group 1（basic diet+0.1% bacterial enzyme preparation） and bacterial enzyme preparation group 2（basic diet+0.2% bacterial enzyme preparation） and bacterial enzyme preparation group 3（basic diet+0.3% bacterial enzyme preparation ）. Each group was set with 5 replicates and 10 lactating cows per replicate.The pre-test period lasted for 7 days and the test period lasted for 42 days.The blood biochemical and immune indexes of lactating cows in each group were analyzed statistically.[Result] ALT,TBIL,CK,ALB,BUN,Na,P,Ca and other blood biochemical indexes of lactating cows in bacterial enzyme preparation group 1,group 2 and group 3 were better than those in control group（P<0.05）. The blood biochemical indexes of bacterial enzyme preparation group 2 were the best.There was no significant difference in IgM,IgG and TNF-α in control group,bacterial enzyme preparation group 1,group 2 and group 3（P> 0.05）. IgA in bacterial enzyme preparation group 2 was higher than that group 1,group 3 and control group（P<0.05）,and there was no significant difference between bacterial enzyme preparation group 1 and group 3（P>0.05）.IL-2 in bacterial enzyme preparation group 1,group 2 and group 3 were higher than that in control group（P<0.05）,and there was no significant difference in IL-2 in group 1,group 2 and group 3（P>0.05）.[Conclusion] Bacterial enzyme preparation could improve the blood biochemical indexes of lactating cows and enhance the immune capacity of the body,and 0.2% was the most suitable addition.