Abstract: The method of basal diets plus amino acid was applied to study the flow and digestibility of amino acid in intestine with different protectedlysine levels of steers. The basal diet was composed of wheat bran, corn and soybean, the nutrition level of energy and protein was supplied according to the nutrition requirement and feed standard of steers. Six healthy crossbred(Limousin×Luxi) steers were selected in the study, which were surgically fitted with permanent fistula in the rumen, the proximal of duodenum and the dismal of ileum. 6×6 Ladin square was adopted in this experiment to study the amino acid flow in duodenum and ileum. The treatments were basal diet plus 0,6,9,12,15 and 18 g/d protectedlysine,respectively.The results showed that the flow of EAA,TAA,Met,Ile,Leu,Lys,Glu in duodenum were increased（P< 0.05）, and digestibility of EAA,TAA,Thr,Cys,Val,Met,Ile,Lys,Ala,Tyr,Pro in intestine were increased（P< 0.05）. This showed that the optimal accession of lysine level is 15 g/d.