Abstract: In order to explore light supplement technology by floating seeding of flue-cured tobacco in winter in Hunan, it was studied for effect on different proportion of red blue to growth of root and leaf and carbon and nitrogen metabolism and enzyme activity of the tobacco seeding.Tests are separately carried out with the light emitting diodes in proportion of blue:red 1:3 ,blue:red 1:1 and blue:red 3:1,and they are combined into different light intensity of light source of tobacco seeding by fluorescent light.The results showed that light quality and light intensity on the tobacco leaf time had little effect,and the growth of tobacco seedings are best when light intensity reaches above 7200 Lux and the proportion of red:blue 3:1.The proportion of red:blue 3:1 can promote chlorophyll synthesis and growth of tobacco seeding,but the proportion of red:blue 1:3 can affect the growth of root and increase root activity. Blue light intensity of the total light intensity between 5% and 15% in the combined light significantly promoted the growth of the stem of tobacco seeding.With the increasing of light intensity, the processing leaf of tobacco seeding of the proportion of red:blue 3:1 in combination source can significantly increase total soluble sugar content and enzyme activity,and the processing leaf of tobacco seeding of the proportion red:blue 1:3 in combination source can significantly increase protein content and nitrate reductase activity.Light quality and light intensity on chlorothyll synthesis and carbon and nitrogen metabolism of tobacco seeding highly has sensitive regulation.Reasonable compensation can promote the growth of root and leaf of flue-cured tobacco seeding.