A field experiment was carried out to investigate the effects of planting density and N application on the yield, photosynthetic characteristics and enzyme activities of tobacco. The results showed that: 1) Planting density and N had a positive interaction with shoot biomass; 2) Planting density, N and planting density×N had no effects on chlorophyll a,chlorophyll b and carotenoids content. Photosynthetic rate had no difference between high and medium density, which was higher than that of low density. Under the condition of high density, the photosynthetic rate of high N was higher than that of medium and low N treatment. Under the condition of medium density, photosynthetic rate at medium N had no difference compared with that at either low or high N. Photosynthetic rate at high N was higher than that at medium N, and photosynthetic rate at low N had no difference with that at medium or high N. Under the condition of low density, photosynthetic rate at high N was lower than that at low N, but photosynthetic rate at medium N had no difference compared with that at either low or high N; 3) Planting density and N had a significant impact on nitrate reductase activities and amylase activities at growing and maturing stages.