Abstract: To reveal the mechanism of nitric oxide (NO) on drought tolerance of flue-cured tobacco under drought stress, a pot experiment was carried out to study the effects of sodium nitroprusside (SNP, an exogenous NO donor) on the chlorophyll content, diurnal variation of photosynthesis, photosynthetic products and nutrient element contents of flue-cured tobacco under drought stress. The results showed that under drought stress, the chlorophyll (Chl) content in flue-cured tobacco significantly decreased. The net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) was reduced, while the intercellular CO₂ concentration (Ci) increased with apparent midday depression of photosynthesis. Simultaneously, the contents of soluble sugar, sucrose, N, and K significantly increased, and the contents of starch, P, Ca, Mg, Fe and Mn significantly reduced. In addition, the contents of B, Zn and Cu were changed slightly. Under drought stress, the application of exogenous SNP (0.25 mmol/L) significantly increased the Chl content in flue-cured tobacco, promoted the Pn, Gs and Tr, and decreased its Ci content. The midday depression of photosynthesis suppressed. The contents of soluble sugar, P, K, Ca, Mg, Fe and Mn raised, however, the sucrose content was significantly reduced, and starch decomposition diminished. Therefore, the exogenous NO could alleviate the adverse effects of drought stress on the capacity of photosynthetic assimilation and the nutrient element absorption of flue-cured tobacco and improve its drought tolerance to a certain extent.