Abstract: UV-B was used to radiate flue-cured tobacco “K326”. Then the effects of different modes and intensities of UV-B radiant on tobacco growth, photosynthetic physiology, pigment, polyphenols, sugar and nicotine contents studied. Results show that tobacco “K326” stem dwarfs and thickens. Also leaf area and net photosynthetic rate moderately decline when flue-cured tobacco “K326” is treated with UV-B radiation. Chlorophyll, sugar and nicotine contents decrease with increasing of UV-B radiant intensity. Chlorophyll content is enhanced by low UV-B radiant intensity. The content of polyphenol in relation to plant stress resistance increases significantly, positively correlated with treatment time and radiant intensity. Pretreatment of rational intensity of UV-B radiant can increase chlorophyll, total carotenoids, and total sugar contents.