A field experiment was conducted using split plot experiment design iethree regimes of planting density（D） as main plots and nitrogen（N） rate as sub plots to investigate the effects of interaction between N application rate and planting density on N and potassium（K） contents，photosynthesis characteristics at round top stage and yield of flue cured tobacco to determine the optimum N application rate and planting density for better growth，higher yield and quality of flue cured tobacco.The preliminary results showed that planting density，N rate and the interaction between them had significant effects on the contents of N，K and carbohydrate contents，net photosynthesis rate（Pn） and yield.Significant positive correlations were obtained between N and K contents，Pn，carbohydrate content of flue cured tobacco at round top stage and yield.Under all three density conditions，the highest yield and N content presented at high N rate treatment，while the greatest contents of K，Pn and carbohydrate at medium N rate treatment.Under all three N rates conditions，the highest yield and K content presented at medium density，while the greatest N content at low density，and the highest Pn and carbohydrate content at low and medium density.In this study，the best combination of N and density treatment was medium density plus high N rate（D2N3），and the appropriate density and N range were 16 078~16 698 plant/hm2 and 8810~10319 kg/hm2 respectively for Qinyan 96.