Abstract: In order to study the effects of different planting densities on morphological structure of tobacco main stem and the transportation and storage of chemical components in the stem, flue-cured tobacco NC55 was used as the material to study the biomass, main stem morphological structure, macronutrients and non-structural carbohydrate content under different planting density treatments in a field experiment. The results showed that the biomass of different organs, especially leaves were reduced by high density treatment. The stem circumference of tobacco treated by high density was 4.28-7.55 cm, the pitch was 1.41-6.13 cm, the stem circumference of tobacco treated by low density treatment was 4.83-10.00 cm, the pitch was 1.26-4.95 cm. Chemical composition analysis showed that the contents of nitrogen, phosphorus and potassium in the main stem decreased from top to bottom, while the contents of soluble sugar, sucrose and starch increased. Under low density treatment, the contents of nitrogen and phosphorus in cortex and pith of main stem were significantly increased and the content of potassium in bottom pith was significantly reduced. Under low density treatment, the contents of soluble sugar, sucrose and starch in the cortex of main stem were increased, and the non-structural carbohydrates in pith were reduced. Low density treatment increased the transportation and storage of nitrogen and phosphorus in the main stem, increased the transportation of non-structural carbohydrates and reduced the storage of non-structural carbohydrates. Planting density changed the transportation and storage capacity of macronutrients and non-structural carbohydrates in the main stem through the morphological structure of the main stem and the proportion of organs, etc. As a result, planting density is an important method to regulate the relationship between source, flow and storage of nutrients in tobacco.