Abstract: In order to explore the influence mechanism of combined application of nitrogen and molybdenum fertilizers on photosynthetic carbon assimilation and nitrogen component accumulation by flue-cured tobacco, using flue-cured tobacco cultivar K326 as the test material, the effects of nitrogen fertilizer to molybdenum fertilizer at different ratios on photosynthetic gas exchange parameters, nitrogen distribution in various organs, nitrogen compounds and dry matter accumulation by flue-cured tobacco were analyzed through pot experiments. The results showed that: 1) The photosynthetic rate of tobacco leaves was significantly improved by increasing the application of molybdenum fertilizer under different nitrogen levels. The net photosynthetic rate of molybdenum fertilizer treatment increased by 9.98% to 58.00% (N₀), 0.86% to 38.39% (N_0.15)and 0.19% to 30.17% (N_0.3), comparing with the treatments without molybdenum fertilizer. 2) The nitrogen accumulation of tobacco plants increased with molybdenum application amount under the moderate and low nitrogen levels, increased by 24.68% to 30.77% (N₀) and 3.69% to 43.47% (N_0.15)respectively as comparing with the treatments without molybdenum fertilizers. However, the nitrogen accumulation under the molybdenum treatment was decreased at high nitrogen level. 3)The dry matter accumulation in the treatment of N_0.15Mo_0.3 was the highest, and the contribution rates of nitrogen, molybdenum and their interaction were 50.60%, 37.65% and 11.75%, respectively. 4)The effects of dry matter accumulation, nitrate reductase activity and free amino acid contents on the changes of total nitrogen and nicotine contents in flue-cured tobacco leaves were significant. The ability of photosynthetic carbon assimilation, the nitrogen absorption and material accumulation could be improved by rational application of nitrogen and molybdenum fertilizers, the nitrogen component content(mass fraction)in cured tobacco leaves could be optimized.