Abstract: In order to clarify the effects of TMV-resistance gene NrCN on photosynthesis and chemical components of transgenic tobacco, T₂ transgenic tobacco plants containing P_ubi.u4::NrCN in the conditions of artificial climate incubators and greenhouse were used as research samples to determine the differential NrCN expression level, chemical compositions and photosynthetic characteristics in transgenic plants. The results showed that transgenic line Q2 with the strongest TMV resistance had the highest NrCN expression level and obvious lesions in leaves. In addition, transgenic line Q1 was stronger. The leaf chemical results indicated that the contents of total alkaloid and total nitrogen in Q2 line before and after topping were significantly lower than those of Q1 and Q3 lines, also lower than the non-transgenic line (P < 0.05). However, chloride ion accumulation in Q2 line was higher before and after topping. The soluble sugar content (14.82 mg·g^-1) in non-transgenic line before topping was significantly (P < 0.01) lower than that in Q1 (21.88 mg·g^-1) and Q2 lines (16.85 mg·g^-1), respectively. Introducing NrCN gene could change the photosynthetic indexes of transgenic tobacco to different extents. Under a low light intensity (1 000 μmol·m^-2·s-^-1), the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of Q1 line increased significantly. Therefore, Q1 line could be used as an ideal parent material for breeding new tobacco germplasms with TMV resistance.