Abstract: By examining the change of free amino acids of plasma and milk in mid-lactation goats,We explord the effect of different crude feed on flow of amino acid (AA) metabolism and milk protein content. Seven mid-lactation goats were divided into two groups randomly and were fed crude ratio diet of 4∶6 (low concentrate group) and 6∶4 (high-concentrate group). Their plasma were obtained from the jugular vein fistula, and milk samples were collected by hand milking. The content of free amino acids of plasma and milk from all goats were detected by RP-HPLC. Total protein concentration in milk was determined by Bradford method. 14 kinds of amino acids were isolated from plasma and 8 kinds of amino acids were detected from milk in two different diet groups. Amino acid composition of the blood or milk between two groups fed different crude feed ratio was no obvious difference Ketogenic amino acid (Leu, Lys), acultative amino acids (Phe, Ile) and branchedchain amino acids (Leu, Ile, and Val) of the blood were significantly or very significantly higher than that in milk. Ala was only amino acid which very significantly lower in blood than in milk. In high-concentrate group, except for Gly and Ala, the contents of the rest amino acids from blood were lower than that of low concentrate group. Total protein concentration in High-concentrate group was slightly higher than that in low concentrate group. but there was no significant difference. It was suggested that free amino acids in blood can provide the raw material and adequate energy for the synthesis of milk protein. When Mid-lactation Goats were fed high concentrate diet, it may not be conducive to increase the content of milk protein and milk production because of low levels of free amino acids in the blood.