Abstract: Objectives Density-increasing and nitrogen-saving are main techniques for high yield and high quality. The feasibility of the density-increasing and nitrogen-saving in flue-cured tobacco production was studied in this paper in South China tobacco-rice rotation field.Methods A field experiment with two factor and three levels was conducted using tobacco cultivar of K326 as materials in Shaoyang tobacco-rice rotation area in Hunan Province. The three density levels were 16667 plant/hm2 (currently used)、18182 plant/hm2 and 20000 plant/hm2,and the three nitrogen application levels were 105, 120 and 135 kg/hm2. The contents of important chemical components in flue-cured tobacco leaves were measured and standardized by the membership function and the principal component analysis method, their weight to construct the chemical composition of tobacco leaf usability index of chemical composition were calculated. The effects of planting density, nitrogen level and their interaction on chemical components of flue-cured tobacco were analyzed by establishing chemical components usability index (CCUI) and adopting partial eta-squared (p2) value.Results The highest chemical availability index was in density treatment of 18182 plant/hm2, in nitrogen treatment of N 120 kg/hm2, and in the combination of density 18182 plant/hm2 with nitrogen 120 kg/hm2 among the respective treatment groups. The combination of density 18182 plant/hm2 and N 135 kg/hm2 showed the second highest chemical availability index. The contribution of nitrogen fertilizer on tobacco chemical components usability was about 46.3%, and that of planting density was about 30.1%, and that of the interaction of planting density and N rate was about 23.6%. Conclusions Nitrogen application rate plays major role in contents of chemical components in tobacco leaves and planting density does the secondary role. Compared with the currently planting density of 16675 plant/hm2 and nitrogen application rate of 135 kg/hm2 in southern China tobacco production areas, it is feasible to increase planting density to 18182 plant/hm2 and reduce nitrogen application rate to 120 kg/hm2.