Abstract: A randomized block experiment was carried out. Two dairy farms that the large scale dairy farm and the park-style dairy cooperative were selected.A total of 80 dairy cows with similar age,body weight,parity,milk production and lactation stage were selected from each farm and then divided into 2 groups,40 Holstein cows in each group.The experiment groups were used to evaluate the effect of supplementation of rumen-bypass amino acid（Lys） on milk production,and milk components. 25 g rumen-protected lysine（RPLys） was added for individual dairy cow in experiment groups.The results showed that comparing with the control group,the milk yield of the experimental groups was increased significant （P﹤0.05）. The milk protein and milk fat percentage were tended to increase（P 0.05）.Other milk components content also increased slightly（P 0.05）.The net income of experiment group was higher than that of control group. The increased net income for experiment group were 1.80 yuan/d,0.52 yuan/d for the large scale dairy farm and the park-style dairy cooperative respectively.