Abstract: In order to clarify the mechanism of the influence of altitude on the formation of fresh-sweet type of flavor compounds and the quality of flue-cured tobacco in Liangshan, tobacco plants in Liangshan tobacco-growing area within the altitude of 1, 300-3, 000 m were studied and factors including appearance quality, sensory quality, routine chemical components, plastid pigments, polyphenols, organic acids, amino acids, carotenoid degradation products and phenylalanine-derived metabolites were systematically analyzed. The results showed that altitude had little effect on appearance quality of flue-cured tobacco, but had a significant effect on the sensory quality and chemical composition of tobacco leaves. Altitude showed a downward-opening quadratic relationship with sensory quality, sugar-to-nicotine ratio, contents of chlorogenic acid and rutin, while an upward-opening quadratic relationship with contents of nicotine, chlorophyll b, citric acid and proline. With increasing altitude, phenylalanine content increased continuously, while contents of phenylalanine metabolites and carotenoid degradation products first increased and then decreased. Tobacco grown at 1, 900-2, 100 m exhibited a prominent fresh-sweet flavor style, superior sensory performance, a balanced sugar-nicotine ratio, enrichment of aroma compounds including polyphenols, carotenoid degradation products and phenylalanine metabolites, and low contents of chlorophyll, organic acids and total amino acids, making this altitude range optimal for the formation of high-quality fresh-sweet flavor type flue-cured tobacco. Therefore 1, 900-2, 100 m was the most suitable planting altitude range for flue-cured tobacco in Liangshan, Sichuan to effectively enhance their sensory quality and fresh-sweet flavor style.