Abstract: The muscle composition of Litopenaeus vannamei cultured at salinity 32 （8.3, 12.5, 16.7 gprawn-1） and cultured in freshwater （12.5 gprawn-1） were analyzed. The result showed that the contents of moisture, lipid,prawn flavor amino acid of the big was lower than that of the small, and the contents of protein, ash, total amino acid, total essential amino acid （EAA）, half EAA, delicious amino acid of the big was higher than that of the small prawns cultured in seawater. The contents of moisture, lipid and unsaturated fatty acid of prawns cultured in freshwater was higher, but the contents of protein, ash, prawn flavor amino acid and delicious amino acid were lower than that of those same scale prawns cultured in seawater. Considering above parameters, nutritional values of the big prawns were higher than the small ones cultured in seawater. The contents of protein, ash, prawn flavor amino acid and delicious amino acid of prawns cultured in seawater were higher than that of those same scale prawns cultured in freshwater.