Abstract: The aim of this study was to study the amino acid composition and nutritional value in different growth stages（squaring stage, flowering stage and grain-filling stage） of Silphium perfoliatum L..Ten plants were randomly selected in the front, middle and back areas of the same plot in the squaring, flowering and grain-filling stage of Silphium perfoliatum L.. After mowing, the samples were heated and smashed to pass through a screen of 60 meshes. The contents of 17 kinds of amino acids（phenylalanine, threonine, valine, alanine, tyrosine, lysine, leucine, glutamic acid, glycine, serine, arginine, isoleucine, aspartic acid, proline, histidine, cystine, methionine） were determined by HPLC in different growth stages of Silphium perfoliatum L.. The amino acid score（AAS）, essential amino acid ratio coefficient（RC）, essential amino acid ratio coefficient score（SRC） and essential amino acid index（EAAI） were measured by FAO/WHO essential amino acid pattern to evaluate the nutritional value in different growth stages of Silphium perfoliatum L.. The results showed that 17 amino acids were detected in different growth stages. There were no significant differences in the amino acids（P＞0.05） between squaring stage and grain-filling stage except for arginine, isoleucine, aspartic acid, proline（P＜0.05）. The differences of amino acids were significant（P＜0.05） at flowering stage compared to squaring stage and grain-filling stage, except for histidine, isoleucine（grain-filling stage）, cystine, methionine, aspartic acid（squaring state）, which were not significantly different（P＞0.05）. The contents of total amino acid were 49.48%（P＜0.01） and 29.48%（P＜0.01） higher in squaring stage and grain-filling stage than in flowering stage, the contents of essential amino acids were 48.80%（P＜0.01） and 33.94%（P＜0.01） higher, the contents of drug-effective amino acids were 47.84%（P＜0.01） and 46.67%（P＜0.01） higher, the contents of sweet amino acids were 57.69%（P＜0.01） and 11.06%（P＞0.05） higher, the contents of fresh amino acids were 35.63%（P＜0.01） and 59.77%（P＜0.01） higher, the contents of bitter amino acids were 52.63%（P＜0.01） and 42.11%（P＞0.05） higher. The values of total essential amino acids/total amino acids and total essential amino acids/total non-essential amino acids were close to the essential amino acid pattern recommended by FAO/WHO at the squaring stage. The highest content of sweet aminoacids was 3.28%, the SRC was 72.18, and the EAAI value was 0.86 at the squaring stage, which reached the standard of good protein source. Lysine was the first limiting amino acid of Silphium perfoliatum L..The results indicated that the amino acids of Silphium perfoliatum L. at the squaring stage were complete, the content of total amino acids was high, and the essential amino acids were relatively balanced and reasonable. It had high content of sweet, sour, and drug-effective amino acids, and had certain medicinal value.