In order to investigate the reasons for the formation of aroma style of quality tobacco leaf and the accumulation of aroma components in flue-cured tobacco, the contents of aroma precursors, including plastid pigments (chlorophyll, lutein, β-carotene) and polyphenols (chlorogenic acid, rutin), and total sugar, reducing sugar, total nitrogen, protein, nicotine, potassium in the upper and middle leaves of flue-cured tobacco exposed to natural light with higher UV-B intensities were determined. The results showed that the synthesis of plastid pigment in upper leaves was suppressed, while that in middle leaves was promoted by intensified UV-B radiation; however, the synthesis of polyphenols was on the contrary. The contents of total sugar, reducing sugar, total nitrogen, protein and nicotine in upper leaves and total sugar and reducing sugar in middle leaves were decreased, while potassium content in upper leaves and the contents of total nitrogen, protein, nicotine and potassium in middle leaves were increased by intensified UV-B radiation. The main aroma precursors and chemical components in flue-cured tobacco were closely correlated to the intensity of UV-B, proper UV-B intensification would improve the aroma and quality of middle leaves of flue-cured tobacco.