Abstract: In order to clarify the differences in chemical compositions in domestic flue-cured tobacco of different leaf structures, the mass fractions of conventional leaf chemical components, polyphenols, organic acids and 21 amino acids in Yunyan 85 tobacco samples of different leaf structures were determined with near-infrared spectroscopy. The results showed that with the leaf structures from compact to loose, 1) the mass fractions of total alkaloids and total nitrogen decreased, while the mass fractions of reducing sugars and total sugars and the ratios of total sugars/total alkaloids and total nitrogen/total alkaloids increased; 2) the mass fraction of chlorogenic acid significantly reduced from relatively loose to loose, the mass fraction of rutin and the total amount of polyphenols increased first and then decreased; 3) in the process of changing from relatively loose to loose, the mass fractions of malonic acid, tetradecanoic acid, linoleic acid and eicosanoic acid significantly decreased, while the mass fraction of levulinic acid significantly increased; 4) the mass fractions of proline, asparagine, glutamine, alanine, serine, glutamic acid, 4-aminobutyric acid, tryptophan, histidine, phenylalanine, threonine, cysteine, tyrosine, arginine, lysine, glycine and leucine, and the total amount of amino acids decreased gradually.