Abstract: To explore a reasonable way of applying magnesium to flue-cured tobacco, a control group without magnesium fertilizer was set up. Four magnesium application treatments were established: base application at the root, topdressing application at the root, base application at the root + topdressing application at the root, and base application at the root + foliar topdressing. The physiological and metabolic differences between the different magnesium application methods and the burley tobacco during the late growth period were compared. The results showed that the potential photosynthesis efficiency and maximum photosynthesis efficiency of the topdressing application at the root treatment were significantly higher than those of the base application at the root treatment, and the base application at the root + topdressing application at the root treatment. The activities of sucrose phosphate synthase, nitrate reductase, glutamine synthetase, superoxide dismutase, catalase, and peroxidase in the topdressing application at the root and base application at the root + foliar topdressing treatments were significantly higher than those in the base application at the root treatment, with increases of 12.29% to 32.20%, 23.38% to 53.90%, 11.43% to 14.29%, 19.86% to 22.70%, 28.30% to 32.08%, and 17.15% to 24.65%. And malondialdehyde and H₂O₂ were significantly lower than those in the base application at the root treatment, with reductions of 5.20% to 6.27% and 5.77% to 20.94%. Applying magnesium fertilizer improved the photosynthesis efficiency and physiological metabolism of tobacco leaves and maintained the stability of leaf cell structure. It also enhanced the antioxidant capacity of leaf cells. In this experiment, topdressing application at the root and base application at the root + foliar topdressing methods of magnesium fertilizer were more beneficial for improving the photosynthetic capacity, carbon and nitrogen metabolism capacity, and antioxidant capacity of tobacco leaves in the later growth period.